This is old news to some, but Ruby now has a great continuous integration story: cruisecontrol.rb. Written by a bunch of Really Smart Guys, it has some innovative features (convention over configuration, no XML, DSL-style tasks, and many more). I mistakenly said in my aboutGroovy Podcast that cruisecontrol.rb supplants the other versions of CruiseControl, but that was clearly wrong: Enterprise CruiseControl was announced recently, which provides consulting, 24x7 support, and new features.
CruiseControl is an example of the best kind of tool: one extracted from real need on a project. The original CruiseControl was developed because developers on a project were feeling build pain and came up with a great solution. Tools are always better when they are derived from real-world experience. Another great example of this is Ruby on Rails. DHH didn't wander over to an ivory tower and think about what a framework should look like. He built some web applications and extracted a framework. Getting developers together to invent frameworks and tools never works as well as taking working stuff and distilling frameworks and tools from it. The classic easy target of how not to do it is EJB 1 and 2: get a bunch of vendors in a room and figure out what developers need (or, more likely, what do we have to sell that we can convince developers they need).
CruiseControl is an ongoing illustration of what happens when you get clever people together who can not only spot a problem but come up with a top notch solution to fix it, then distill the results.