The features we like most...

• Forms designer for C#, VB.NET and Boo
• Code completion for C#, VB.NET and Boo (including Ctrl+Space support)
• Integrated NUnit support plus code coverage (NCover)
• Integrated debugger
• Code Analysis with FxCop
• Refactoring support
• Multi-framework support (.NET 1.1 and 2.0, Mono, Compact Framework)
• XML Editing (source and tree view) with XPath search
• Parser-based code converter (C# to VB.NET / Boo and more)
• Compile C#, VB.NET & Boo code in the IDE out-of-the-box
• Code AutoInsert (Alt+Ins)
• Xml documentation preview
• Setup projects supported with Windows Installer XML (WiX)
• Subversion integration
• Open source, LGPL licensed

And here are some more...

• User interface translated to many languages
• Write C#, ASP.NET, ADO.NET, XML, HTML code
• Project or File-based development (Project Scout & File Scout)
• Rich project options
• Syntax highlighting for C#, HTML, ASP, ASP.NET, VBScript, VB.NET, XML
• Intelligent braces
• Folding
• Bookmark your code
• Code template support
• Component Inspector
• Feature-rich Find & Replace dialogs (including incremental search)
• Easily extensible with external tools
• Easily extensible with Plug-Ins
• Re-host SharpDevelop with SDA
• ... and much more

If you like to see the features in action, then take our Feature Tour.