Where can I get OctaForge?
There are builds for Linux and Windows. Each build contains native binaries for x86 and x86_64. There is a debug and a release variant for each, too. Besides that there are source snapshots generated from the same source the binaries are built from. The tar.xz version is a plain snapshot, the zip version contains Windows build dependencies pre-bundled.
What operating systems are supported?
Linux is well supported.
Windows is also supported on both 32 and 64 bits. It gets less testing than the other supported OSes at this point.
Mac OS X is not officially supported right now, but it should work. Sadly, it cannot be supported as I don't have a Mac to test things on. I'll try to change that soon.
FreeBSD is supported, there are no autobuilds because it's impossible to crosscompile for FreeBSD from Linux. FreeBSD users are advised to build themselves.
Solaris (Solaris, Illumos, OpenIndiana, ...) should work, but is not tested. If you're willing to test and report, I can put it on the official list.
Other BSDs (OpenBSD, NetBSD, ...) should also work, assuming you have a sufficient graphics card (latest Haswell Intel GPUs with Mesa should suffice). Same as for Solaris applies - if you're willing to test and report for your particular OS, it can be put on the list.
How to run it?
To run OctaForge, read README.txt in the archive. If you're compiling, you might want to read INSTALL.txt as well. Please note that the builds and the engine overall is intended primarily for developers.
Thank you for being interested in OctaForge and maybe giving it a shot. It's much appreciated and is what drives development forward.