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The corefx repo contains the library implementation (called "CoreFX") for .NET Core. It includes System.Collections, System.IO, System.Xml and many other components. It builds and runs on Windows. You can 'watch' the repo to see Linux and Mac support being added over the next few months.

You can also see more information in the Documentation README.

.NET Core is a modular implementation of .NET that can be used as the base stack for a wide variety of scenarios, today scaling from console utilities to web apps in the cloud. You can learn more about .NET Core and how and where you can use it in the .NET Core is open source and Introducing .NET Core blog posts.

The .NET Core Runtime repo contains the runtime implementation (called "CoreCLR") for .NET Core. It includes RyuJIT, the .NET GC, native interop and many other components.

Runtime-specific library code - namely mscorlib - lives in the CoreCLR repo. It needs to be built and versioned in tandem with the runtime. The rest of CoreFX is agnostic of runtime-implementation and can be run on any compatible .NET runtime. These characteristics were the primary motivation for the 2-repo structure.

Some of the best ways to contribute are to try things out, file bugs, and join in design conversations.

Want to get more familiar with what's going on in the code?

• Pull requests: Open/Closed
• , and changes

Looking for something to work on? The list of up-for-grabs issues is a great place to start or for larger items see the list of feature approved. See some of our guides for more details:

• Contributing Guide
• Developer Guide
• Issue Guide

You are also encouraged to start a discussion by filing an issue or creating a gist.

You can discuss .NET OSS more generally in the .NET Foundation forums.

Want to chat with other members of the CoreFX community?

The repo currently contains the source for the following components. More libraries are coming soon (the overall list of items we currently plan to move onto GitHub is here). 'Watch' the repo to be notified.

Component	Description
System.Collections	Provides classes that define generic collections, which allow developers to create strongly-typed collections.
System.Collections.Concurrent	Provides a set of thread-safe collection types, instances of which may be used concurrently from multiple threads.
System.Collections.Immutable	Provides a set of immutable collection types that are safe to use concurrently.
System.Collections.NonGeneric	Provides classes that define various collections of objects, such as ArrayList and Hashtable. These collections exist in .NET Core primarily for backwards compatibility and generally should be avoided when writing new code.
System.Collections.Specialized	Provides classes that define specialized collections of objects, for example, a linked list dictionary and collections that contain only strings. These collections exist in .NET Core primarily for backwards compatibility and generally should be avoided when writing new code.
System.ComponentModel	Provides interfaces for the editing and change tracking of objects used as data sources.
System.ComponentModel.Annotations	Provides attributes that are used to define metadata for objects used as data sources.
System.ComponentModel.EventBasedAsync	Provides support classes and delegates for the event-based asynchronous pattern. This pattern and these supporting types exist in .NET Core primarily for backwards compatibility and generally should be avoided when writing new code.
System.ComponentModel.Primitives	Provides interfaces that are used to implement the run-time and design-time behavior of components.
System.ComponentModel.TypeConverter	Provides the System.ComponentModel.TypeConverter class, which represents a unified way of converting types of values to other types.
System.Console	Provides the Console class, which enables access to the standard input, output, and error streams for console-based applications.
System.Diagnostics.Contracts	Provides types and methods for representing program contracts such as preconditions, postconditions, and invariants.
System.Diagnostics.Debug	Provides a class to interact with the debugger as well as methods for performing runtime assertions.
System.Diagnostics.FileVersionInfo	Provides useful functionality for querying and examining the version information of physical files on disk.
System.Diagnostics.Process	Provides access to local and remote processes, and enables the starting and stopping of local system processes.
System.Diagnostics.TextWriterTraceListener	Provides trace listeners for directing tracing output to a text writer, such as System.IO.StreamWriter.
System.Diagnostics.Tools	Provides attributes, such as GeneratedCodeAttribute, that are emitted or consumed by analysis tools.
System.Diagnostics.TraceSource	Provides classes that help you trace the execution of your code.
System.Dynamic.Runtime	Provides classes and interfaces that support the Dynamic Language Runtime (DLR).
System.Globalization.Calendars	Provides classes for performing date calculations using specific calendars, including the Gregorian, Julian, Hijri and Korean calendars.
System.Globalization.Extensions	Provides classes for performing unicode string normalization, culture-specific string comparisons and support the use of non-ASCII characters for Internet domain names.
System.IO	Provides base input and output (I/O) types that enable reading and writing data streams.
System.IO.Compression	Provides classes that support the compression and decompression of streams.
System.IO.Compression.ZipFile	Provides static methods for creating and using Zip files.
System.IO.FileSystem	Provides access to the file system, including support for enumerating and manipulating file system objects and for reading and writing files via streams.
System.IO.FileSystem.DriveInfo	Provides the System.IO.DriveInfo class, which enables developers to query local drive information.
System.IO.FileSystem.Primitives	Provides common enumerations and exceptions for path-based I/O libraries.
System.IO.FileSystem.Watcher	Provides the System.IO.Watcher class, which listens to the system directory change notifications and raises events when a directory or file within a directory changes.
System.IO.MemoryMappedFiles	Provides access to memory-mapped files, enabling code to read and write files by reading and writing memory.
System.IO.Packaging	Provides classes that support storage of multiple data objects in a single container.
System.IO.Pipes	Provides types that enable a means for interprocess communication through anonymous and/or named pipes.
System.IO.UnmanagedMemoryStream	Provides a stream for accessing unmanaged memory as represented by a pointer, as well as an accessor for reading and writing primitive types from unmanaged memory.
System.Linq	Provides the foundation of Language-Integrated Query (LINQ), including LINQ standard query operators that operate on objects that implement IEnumerable<T>.
System.Linq.Expressions	Provides classes, interfaces, and enumerations that enable language-level code expressions to be represented as objects in the form of expression trees.
System.Linq.Parallel	Provides a parallelized implementation of LINQ to Objects. "Parallel LINQ" (PLINQ) implements the full set of LINQ standard query operators as well as additional operators specific to parallel operations.
System.Linq.Queryable	Provides LINQ standard query operators that operate on objects that implement IQueryable<T>.
System.Net.Http	Provides a programming interface for modern HTTP applications, including HTTP client components that allow applications to consume web services over HTTP and HTTP components that can be used by both clients and servers for parsing HTTP headers.
System.Numerics.Vectors	Provides a set of basic vector types that leverage single instruction, multiple data (SIMD) CPU instructions.
System.ObjectModel	Provides types and interfaces that enable the creation of observable types that provide notifications to clients when changes are made.
System.Reflection	Provides types that retrieve information about assemblies, modules, members, parameters, and other entities in managed code by examining their metadata.
System.Reflection.DispatchProxy	Provides a mechanism for dynamically creating proxy types that implement a specified interface and derive from a specified DispatchProxy type.
System.Reflection.Emit.ILGeneration	Provides types that allow a compiler or other tool to emit Microsoft intermediate language (MSIL).
System.Reflection.Emit.Lightweight	Provides the System.Reflection.Emit.DynamicMethod class, which represents a dynamic method that can be compiled, executed, and discarded.
System.Reflection.Extensions	Provides custom attribute extension methods for System.Reflection types.
System.Reflection.Metadata	Provides a highly-tuned, low-level ECMA-335 metadata reader. This is the same reader used by "Roslyn" C# and Visual Basic compilers to parse assemblies.
System.Reflection.TypeExtensions	Provides extension methods for types in the System.Reflection namespace. These extensions are designed to be source-compatible with older reflection-based APIs.
System.Resources.ReaderWriter	Provides classes for reading and writing resources in the system-default format.
System.Runtime	Provides the fundamental primitives, classes, and base classes that define commonly-used value and reference data types, events and event handlers, interfaces, attributes, and exceptions.
System.Runtime.Environment	Provides types that expose information about the runtime and operating system environment in which code is executing.
System.Runtime.Extensions	Provides commonly-used classes for performing mathematical functions, conversions, string comparisons, and querying environment information.
System.Runtime.Handles	Provides base classes, including CriticalHandle and SafeHandle, for types that represent operating system handles.
System.Runtime.InteropServices	Provides types that support platform invoke (P/Invoke) and COM interop.
System.Runtime.Numerics	Provides two useful numeric structures, BigInteger and Complex.
System.Runtime.Serialization.Json	Provides classes for serializing objects to the JavaScript Object Notation (JSON) and for deserializing JSON data to objects.
System.Runtime.Serialization.Primitives	Provides common types, including System.Runtime.Serialization.DataContractAttribute, for libraries that support data contract serialization.
System.Runtime.Serialization.Xml	Provides classes for serializing objects to the Extensible Markup Language (XML) and deserializing XML data to objects.
System.Security.Cryptography.DeriveBytes	Provides the System.Security.Cryptography.Rfc2898DeriveBytes class, which implements password-based key derivation functionality per RFC 2898.
System.Security.Cryptography.Encoding	Provides types for representing Abstract Syntax Notation One (ASN.1)-encoded data.
System.Security.Cryptography.Encryption	Provides base types for symmetric and asymmetric cryptographic algorithms.
System.Security.Cryptography.Encryption.Aes	Provides types which perform symmetric encryption and decryption using the Advanced Encryption Standard (AES) algorithm.
System.Security.Cryptography.Hashing	Provides base types for cryptographic hashing and hash-based message authentication code (HMAC).
System.Security.Cryptography.Hashing.Algorithms	Provides concrete implementations of cryptographic hashing and hash-based message authentication code (HMAC), including MD5, SHA-1, and SHA-2.
System.Security.Cryptography.RandomNumberGenerator	Provides the System.Security.Cryptography.RandomNumberGenerator class, which generates cryptographically secure random numbers.
System.Security.Cryptography.RSA	Provides types which perform asymmetric encryption and decryption using the RSA algorithm.
System.Security.Cryptography.X509Certificates	Provides types for reading, exporting and verifying Authenticode X.509 v3 certificates.
System.Security.Principal	Provides the base interfaces for principal and identity objects that represent the security context under which code is running.
System.Security.Principal.Windows	Provides classes for retrieving the current Windows user and for interacting with Windows users and groups.
System.Security.SecureString	Provides support for accessing and modifying text that should be kept confidential.
System.ServiceProcess.ServiceController	Provides the ServiceController class that represents a Windows service and allows you to connect to a running or stopped service, manipulate it, or get information about it.
System.Text.Encoding	Provides base abstract encoding classes for converting blocks of characters to and from blocks of bytes.
System.Text.Encoding.CodePages	Provides the ability to access existing encoding types for string manipulation across common cultural standards, as well as support to create custom Encoding Providers.
System.Text.Encoding.Extensions	Provides support for specific encodings, including ASCII, UTF-7, UTF-8, UTF-16, and UTF-32.
System.Text.Encodings.Web	Provides support for encodings related to HTML, JavaScript, and URLs.
System.Text.RegularExpressions	Provides a regular expression engine. The types in this library provide useful functionality for running common operations using regular expressions.
System.Threading	Provides synchronization primitives used when writing multi-threaded and asynchronous code.
System.Threading.Tasks	Provides types that simplify the work of writing concurrent and asynchronous code.
System.Threading.Tasks.Dataflow	Provides a set of types that support actor/agent-oriented designs through primitives for in-process message passing, dataflow, and pipelining.
System.Threading.Tasks.Parallel	Provides library-based data parallel replacements for common operations such as for loops, for each loops, and execution of a set of statements.
System.Xml.ReaderWriter	Provides types for reading and writing streams of XML.
System.Xml.XDocument	Provides XML-related types for querying XML documents using LINQ.
System.Xml.XmlDocument	Provides types for manipulating an XML Document Object Model (DOM).
System.Xml.XmlSerializer	Provides classes for serializing objects to XML and for deserializing XML data to objects.
System.Xml.XPath	Provides classes that define a cursor model for navigating and editing XML information items as instances of the XQuery 1.0 and XPath 2.0 Data Model.
System.Xml.XPath.XDocument	Provides extension methods that add System.Xml.XPath support to the System.Xml.XDocument package.
System.Xml.XPath.XmlDocument	Provides extension methods that add System.Xml.XPath support to the System.Xml.XmlDocument package.
Microsoft.CSharp	Provides support for compilation and code generation, including dynamic, using the C# language.
Microsoft.VisualBasic	Provides types that support the Visual Basic runtime.
Microsoft.Win32.Primitives	Provides common types supporting the implementation of Win32-based libraries.
Microsoft.Win32.Registry	Provides support for accessing and modifying the Windows Registry.

.NET Core (including the corefx repo) is licensed under the MIT license.

.NET Core is a .NET Foundation project.

There are many .NET related projects on GitHub.

• The .NET home repo links to 100s of .NET projects, from Microsoft and the community.
• The .NET Core repo links to .NET Core related projects from Microsoft.
• The ASP.NET home repo is the best place to start learning about ASP.NET 5.
• dotnet.github.io is a good place to discover .NET Foundation projects.