In Java, there are quite a number of CI tools available, e.g. Hudson, Continuum, CruiseControl, and LuntBuild. For .NET, there are also few open source CI tools that can be used.
CruiseControl.NET is an Automated Continuous Integration server, implemented using the Microsoft .NET Framework.
A list of tools that CruiseControl.NET can integrate with can be read at Using CruiseControl.NET with other applications.(CVS,SVN,NAnt, MSBuild, NUnit, …)
Draco.NET is a Windows service application designed to facilitate continuous integration. Draco.NET monitors your source code repository, automatically rebuilds your project when changes are detected and then emails you the build result along with a list of changes since the last build.
Draco.NET version 1.5 supports builds using NAnt build tool or via Visual Studio .NET 2002/2003 solution files. Draco.NET can monitor Source Control repositories in CVS, Visual SourceSafe, PVCS, SubVersion, and others.
A nice comparison can be found at TheServerSide.