FS-UAE should now be available in the ports tree for both FreeBSD and OpenBSD 🙂 Please note that I’m not involved in these projects and may not be able to help with questions specific to these ports.
The download page has been updated with this information!
FS-UAE is currently only available for Windows, Mac OS X and Linux. However, it should be relatively easy to get it to compile and run on FreeBSD as well.
If you are a FreeBSD user and want to use and test FS-UAE, please leave a comment! I won’t bother to implement support for FreeBSD unless there is some demand for it.