I found most people talk about Hudson for simple and free continuous integration. Now personally I'm not fond of its interface which I find very messy, and I found almost no one talking about CDash -- I love CMake and CTest seem nice too.
Could you give for your favorite continuous integration server/builder/tester/dashboard a short description of its strong and weak decision points.
Here is a list of free (in the broad meaning for a small-medium project) those I've heard of, or used:
Environment: C++, C#, Python, PHP... can be various.
PS: Preferably give one answer per tool or comment on it there is already one.