Some time ago I tried to get the XtreemFS server to work on MacOSX (Lion).
I had to patch it a bit to make it compile and run. So here's the patch if you want to give it a try:
I wanted to use it to have a synchroneous replicated filesystem over a WAN but in the end I gave up this idea and switched to unison.
Btw. I also tried to get gluster fs to work on MacOSX lion and partially succeeded. You can see my changes on github