Buildbot
I'd set up buildbot at a customer last monday. Since that resulted in me understanding the thing, I also set up an instance for nbd. The need for this had become apparent after the last upload to unstable failed on a disconcertingly large number of architectures.
Apart from the fact that it uses python (and wants me to write python in its config file, grrr), it's a fairly nice system; pretty lightweight (it runs on barbershop, which is a QNAP TS419U, for crying out loud), yet still flexible enough that I don't have to jump through hoops to do normal things which the developer hadn't thought about.
I also just noticed that if you push multiple commits to a git repository at once (put otherwise, if buildbots notices multiple new revisions when it checks), it will make sure that all revisions get built at least once. Of course it would have been nice if it would pick the fastest machines to do the "older" revisions rather than "whoever happens to be first", but that doesn't really matter all that much.
Meanwhile, the bug that makes building 3.6 impossible on some architectures has been fixed. It turned out to be an LFS-issue, which is specific to 32-bit machines; and as my own machine runs amd64, well...