as usual with java world, there is the open source world and the commercial world.
We've already seen pretty good coverage of the various offerings.
Hudson : I don't know of a single other java server offering that is as easy as this to evaluate. java -jar hudson.war -- how easy can it get than that ? NOT only can you use it on windows, you can use it on all the usual java platforms. Ant, Maven and a host of other build platforms are supported.
The best thing about Hudson is the plug-in capability. It is being developed almost continuously. You ask for a feature and it won't take long for it to be done.
I usually don't like sounding like a fanboy, but this app/developer/community sure impresses me.
BR,
~A