Open-source OPC UA client and server library for .NET based on IEC 62541. Available as only source files, a demo client and a demo server. Tested and commercially used in industrial applications with commercial vendors' UA servers and clients.

• Fully supported OPC UA core client and server specification.
• OPC UA binary protocol with chunking.
• Optimized memory buffers for encoding/decoding large and complex structures to/from raw bytes.
• Support for all message types, node types, and default address space from the UA specification.
• Support for signing and encrypted security profiles.
• Anonymous, user/pass and certificate-based authentication.
• Sessions, subscriptions (data change notifications and custom notifications), custom events and alarming.
• Extendable server address space with hooks for client requests for access control, read handlers, write handlers, etc.
• Support for reads, writes, updates, historical data and aggregation.
• Server instances have low overhead: tested with hundreds of clients performing simultaneous historical reads, data change notification subscriptions and real-time writes.

Free for commercial use under the Apache License 2.0. Please give credit if you find this source useful.