MonoDevelop

MonoDevelop is a free GNOME IDE primarily designed for C# and other .NET languages. The main features of MonoDevelop are:
    * Code Completion. MonoDevelop's intelligent code completion attempts to complete type, method and field names as you're typing. The IDE will automatically get the class information from your source code files and from the libraries referenced in your project.
    * Class Management. MonoDevelop has a class viewer which allows you to list the classes in your project, their methods, and properties. Your namespaces are also kept track of to keep the classes separated.
    * Built-in Help. The .NET documentation and the Gtk# documentation are built into MonoDevelop for easy access.
    * Project Support. MonoDevelop comes with built in projects that help get you started with your console, Gnome# or Gtk# application.
    * Add-ins. MonoDevelop has a powerful add-in engine, which together with a modular API and a complete set of extension points, provides a seamless platform upon which to build your own development tools. MonoDevelop also provides an Add-in Manager you can use to install add-ins from online repositories.

Go to http://www.monodevelop.com/

See also these related projects.