I worked on the Mac OS X backend... or more precisely, i rewrote the Mac OS X backend from scratch. This was done to remove the Xcode dependency - everything is now built from a Makefile. This also made the OS X code *much* smaller (only a couple of files instead of a bunch of resources, files, classes, etc generated by Xcode) and fixed a couple of issues i had. Also implemented fullscreen mode (although it doesn't change resolution yet) and, most importantly, raw mouse input. I think my engine is one of the few engines on Mac OS X to do raw mouse input since a lot of games seem to be affected by mouse acceleration. This was done by registering a callback with the HID API introduced in OS X 10.5 (and is very badly documented - probably why many people miss it) and checking for mouse motion events there (the button press and release events are still done in the regular event loop).
Another thing that i managed to do today was to setup cross-compiling for OS X from Linux, so now with a single script under Linux i can make builds for Linux, Windows and Mac OS X (32 and 64 bit for all except Windows which only has 32 bit builds since Windows has good 32-on-64 bit support). The .tar.xz i updated in the original post was made using this script. This was also the reason i wanted to remove the Xcode dependency. I used the osxcross project to build the crosscompiler (i also had to build a recent version of Clang because the one bundled with Debian Jessy is too old to be used with the latest OS X SDK).
I also added a cvar to limit the framerate. Can be helpful if you are near the 60fps that the engine updates (e.g you get 70 or 80fps) at and it doesn't feel smooth. It can be enabled with enabling the console with ~ and typing cset fpslimit 60 (or any other value). Alternatively enabling vsync might help, although the only OS so far i've seen vsync to feel good is OS X (where it feels almost perfect). I'll need to investigate that.
Game-wise there seems to be a bug with the particles not spawning in some cases in the Windows version when it is run under Windows (ie. it doesn't happen under Wine). Those are always fun to debug :-/.