We've also ported it to Linux.
Gazebo requires pthreads.
There is a forking version which uses pthreads less heavily than the non-forking version and thus may be more stable on systems with poor threading. XML parsing is handled by a special parser with a limited feature set. Please contact us if you succeed in porting it to other UNIX flavors. Compiling Gazebo is distributed as a gzipped tar archive. Gazebo comes with an example configuration file which should get you started.