#develop (short for SharpDevelop) is a free IDE for C# and VB.NET
projects on Microsoft's .NET platform. It is open-source (GPL).
While Eclipse is perhaps a bit more feature rich SharpDevlop is
really fun to work with. The only disadvantage is, that it doesn't
run on Linux/Mono, because it builds on System.Windows.Forms, that
are not ready, yet.
Strengths about SharpDevelop:
Completely written in C#
Compile C# and VB.NET in the IDE out-of-the-box
Open source, GPL licensed
Lightweight IDE
Code completion
Forms designer
User interface translated to many languages
Everything templated: add new project or file types, or even
compilers to SharpDevelop
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
Bookmark your code
Code template support
Feature-rich Find & Replace dialogs
Easily extensible with external tools
Easily extensible with Plug-Ins
... and much more
For more information about SharpDevelop and download refer to
this