jGRASP is a lightweight development environment, created specifically to provide automatic generation of software visualizations to improve the comprehensibility of software
Pydev is a plugin that enables users to use Eclipse for Python and Jython development -- making Eclipse a first class Python IDE -- It comes with many goodies such as code completion, syntax highlighting, syntax analysis, refactor, debug and many others. If you want more details on the provided features, you can check here.
SharpDevelop, acortado a #Develop, es un IDE gratuito para C#, VB.NET y Boo projects sobre la plataforma de Microsoft .NET. Dado que se trata de un software de código abierto puedes descargarlo y examinar el código fuente, así como los ejecutables desde su sitio web.