The builds can be fetched from here:
Trunk builds, rebranded as "Armagetron Experimental"
0.2.8 builds, rebranded as "Armagetron Alpha"
hack builds, mostly sty+ct, various rebrandings.
Read here what quality to expect from those builds. tl;dr: not much

The rebranding makes it so that you can install versions from different branches somewhat independently from each other and from our main, stable releases. On Windows and Linux, installation is independent with different default installation directories, separate uninstallers and start menu entries. On Linux only currently, your user configuration will be independent for different brandings.
If there are no build errors, every build should contain 32 and 64 bit Linux binaries and 32 bit Windows binaries, they are all automated. Mac builds are not done every week, I need to boot up a different machines for those. And if they are done, they are usually uploaded with a delay of no more than one release.
Ubuntu and Debian users can also just use our PPA, all the automatic builds are uploaded to there, too, as the armagetronad-alpha and armagetronad-experimental packages. If you don't want to add the PPA to your software sources, you can manually download current packages (sources, too) on the package detail page. Just expand the various packages to get to their content list.
I currently cannot build Trunk Mac releases. Sorry. Will work on it.