This control allows a linked form control to be dynamically expanded and collapsed by clicking on the splitter control button, and resized by dragging the splitter.

Homepage at:CodeProject.com

Sqlite is a library that offer embedded database capabilities, it's a mature project and I uses it to store all my application setting in an easy to query way.
Sqlite.Net is the ADO.Net provider for sqlite and allows the use of sqlite from .net applications.

Homepage at: Sqlite.org
Sqlite.net at: source forge.

Log4net is a logging library that has its roots in Log4j. It offer runtime configuration of logging and many types of loggers.
Homepage at: logging.apache.org/log4net/

An object / relational mapper with root in Java's Hibernate. Extensible, simple, easy to use and very powerful. I found that I'm far more productive with it.

Homepage at: NHibernate.org

NAnt is a port of Ant to the .Net platform, it offer rich, XML based, syntax to building your projects. Useful in continous integration scenarios.

Homepage at: Nant.sf.net

NCover is a tool to help you find out your test coverage, it uses the profiler API, so you don't need to modify your tool.

Hompage at: Ncover.org

Makes creating sophisticated UI very easy.

Homepage at: http://sourceforge.net/projects/dockpanelsuite/

Allows to easily display graphs and manipulate them. A modified version of their control is used in NHibernate Query Analyzer.
Lithium is a subset of the Netron Library.

Homepage at: http://netron.sf.net

The ubiqious framework, and the one everyone seems to be using. Doesn't have as many capabilities as MbUnit, but has good support and easy extensibility.

Homepage at: NUnit.org

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Homepage at: MbUnit.tigris.org