SharpDevelop is a free, open-source, IDE for C#, VB.NET and Boo projects on Microsoft's .NET Platform. Version 4.0 has just been released and supports .NET 4.0.
SharpDevelop 4.0, developed under the code name "Mirador", is based on .NET Framework 4.0, released in April 2010. The programming environment requires .NET 3.5 SP1 and the development team recommends using the Windows SDK.
The IDE can be used to create .NET and Mono programs in C#, Visual Basic, Boo, IronPython, IronRuby and F#. The workbench has been rewritten to be able to utilise the Windows Presentation Foundation (WPF) graphics framework instead of Windows Forms. The text editor, AvalonEdit, is also new and is, like the text editor in Microsoft's Visual Studio 2010, is based on WPF.
Other new features include the WPF and Entity Framework designers, support for Visual Basic .NET 10 and C# 4.0, automatic code completion in IronPython and the integration of unit testing into IronPython and IronRuby.
It also features an add-in for using open source distributed version control system Git and there is the Usage Data Collector, inspired by the Eclipse development environment, which aims to let the SharpDevelop team know which functions users actually use – it is disabled by default.
As a "bet you didn't know" sort of fact - the C# to VB Code Conversion tool available in the Resources section of I-Programmer uses SharpDevelop. You can discover how this utility was created and download its code - Code conversion (C#/VB) in Silverlight.