The UnitTests can be executed to generate Excels in bin/Debug/excels. (Some tests even contain assertions!)

# Install last free version:
Install-Package EPPlus -Version 4.5.3

# Install commercial version:
Install-Package EPPlus

• Basic usage
• Loading & saving
• Selecting cells
• Writing values
• Formatting sheets, columns and cells
• Conditional formatting

• BasicFormulas
• DataValidation
• Attaching a logger to the FormulaParser

Loading data from

• LoadFromCollection & LoadFromArrays (IEnumerable)
• LoadFromDataTable & DataReader
• LoadFromText (CSV)

• Printing
• Workbook properties
• Converting Excel Addresses
• Adding comments & rich text
• Protection against edit

• String manipulation
• Numbers & Math
• Date & Time
• Boolean logic

Don't seem to work for LibreOffice. Example code can be found in the official EPPlus examples.

• Sample4.cs: Basic example
• Sample5.cs: A pie
• Sample6.cs: Pretty nifty, worth checking out!

They also have a chart example on their main documentation.

Will we cover these also, sometime?

• ConditionalFormatting in more detail: See Sample14.cs
• Filtering
• Grouping and ungrouping
• Tables
• Inserting VBA: See Sample15.cs
• Numberformat.Format = [$$-409] --> Get info on those numbers
• 1-QuickTutorial ExcelPrinting: insert a company picture in the print footer: sheet.HeaderFooter.EvenHeader.InsertPicture()
• Password protection: Add Encryption
• WebApi integration and calling code for Superagent, Angular Http and Fetch? :)

WebApi:

public class ExcelResult : ActionResult
{
    public string FileName { get; set; }
    public ExcelPackage Package { get; set; }

    public override void ExecuteResult(ControllerContext context)
    {
        context.HttpContext.Response.Buffer = true;
        context.HttpContext.Response.Clear();
        context.HttpContext.Response.AddHeader("content-disposition", "attachment; filename=" + FileName);
        context.HttpContext.Response.ContentType = "application/vnd.ms-excel";
        context.HttpContext.Response.BinaryWrite(Package.GetAsByteArray());
    }
}

Adding a picture:

Bitmap icon = GetIcon(dir.FullName);
ws.Row(row).Height = height;
if (icon != null)
{
    ExcelPicture pic = ws.Drawings.AddPicture("pic" + (row).ToString(), icon);
    pic.SetPosition((int)20 * (row - 1) + 2, 0);
}