CruiseControl

CruiseControl is written in Java but is used on a wide variety of projects
There are builders supplied for Ant, NAnt, Maven, Phing, Rake, and Xcode, and the catch-all exec builder that can be used with any command-line tool or script

CruiseControl is open source software and is developed and maintained by a group of dedicated volunteers
CruiseControl is distributed under a BSD-style license

The CruiseControl wiki has extensive additional documentation for CruiseControl, including a list of 3rd Party Tools that work with CruiseControl

Two such projects are ConfigurationGUI and CCScrape
ConfigurationGUI is a Java WebStart Swing GUI for creating cruisecontrol configuration files and monitoring project status
It is bundled with the binary distribution of CruiseControl but can also be downloaded separately
CCScrape is a Java WebStart application that makes easy work of driving XFDs (eXtreme Feedback Devices) from your CruiseControl build results

There are ports of CruiseControl for
NET and Ruby
The original CruiseControl source code was contributed by ThoughtWorks, who now offers the commerical tool Cruise (not based on the CruiseControl codebase)