Toolforge is a hosting environment for developers working on services that provide value to the Wikimedia movement. These services allow developers to easily do ad hoc analytics, administer bots, run webservices, and generally create tools to help editors and other volunteers in their work. The environment also includes access to a variety of data services.
The Toolforge community-developed web applications are all listed at tools.wmflabs.org. There is also a smaller selection listed in more detail at Hay's Tools Directory.