While looking around for automated build systems years ago, I stopped at buildbot - http://buildbot.net/

Buildbot never stopped surprizing me in the good way.

Probably one of the best usage is at Chromium Project - http://build.chromium.org/p/chromium/waterfall

While I try to design and implement Continuous Integration pilot on Clearcase/UCM repository, many challenges are on-going and with buildbot one can handle them quite easy.

The software is open source, still it was not trivial to find example of some "advanced" usage.

Below is the **nextSlave** function I'm using, that hopefully will choose the slave with lowest number of running builds that **can** acquire the configured slave locks:

<code>
def getNbOfActiveBuilders(slaveBuilders):
   active_builders = [sb for sb in slaveBuilders.slave.slavebuilders.values()
                      if sb.isBusy()]

   return len(active_builders)
   

def myNextBuildSlave(builder, slaveBuilders):
   slaveBuilders.sort(key=lambda s: getNbOfActiveBuilders(s))
   for sb in slaveBuilders:
      if builder.canStartWithSlavebuilder(sb): #check locks before
         return sb
   return None

</code>