JNOS 2.0 has made it to 4 different operating systems in one way or another ...
Linux is still the primary platform. The linux version of JNOS 2.0 is the one on which I do all my development. It gets all the attention, updates, and so on.
DOS still has a user base, and is still supported in the sense that I try to update it to the same version as the linux version when time permits, although it's been over 3 years now since the last release. The DOS version has fallen behind, and of course not all the features can be included, because the features are specific to linux or the kernel itself.
WIN32 started off as a concept project, but recently I have decided to take it to a more practical and functional piece of software. The original demo programs of 2007 saw me taking the core parts of JNOS 2.0 and porting them to the WIN32 (native windows) environment. The project was pretty cool, and I was able to show it was possible. It was actually quite easy to do. After a 5 year absence, it is once again an active project. A lot of stuff has not been ported over (yet). This will run on both XP and Windows 7.
Mac OS/X is a port for Mac OS/X (Darwin) on PowerPC machines. This is dated, it was last worked on in 2006.