An unit testing framework that is open source written in C#.

An open source photo editor that teaches many aspects of Windows forms development. Written entirely in C# the source code is under an MIT open license agreement.

An application framework that provides capabilities like dependency injection and Aspect Oriented Programming (AOP) for building enterprise .NET applications.

An open source integrated development environment written in C#.

mojoPortal is an open source content management system and web site framework portal for .NET.

A embeddable .NET based workflow framework

A toolkit that supports the development of 2D structured graphics programs allowing for Zoomable User Interfaces (ZUIs).

An open source PHP compiler written in .Net.

The MonoUML Project aims to develop a CASE tool for GNU/Linux and UNIX environments, using Mono as development and running framework.

OpenXML Writer is an opensource text editor for creating WordprocessingML files (.docx) that is created with the .Net Framework.