Btrfs (which I pronounce as Betterfs) is a new Linux filesystem with many of ZFS's design sensibilities. It's being developed by Chris Mason from Oracle and was announced about half a year ago - the lkml announcement thread has some interesting posts.
How did I miss this until now? :-? Regardless, this is great news for Linux and Linux users. With ZFS entering the BSDs and OSX, Linux looked like it was going to be left behind. This is some great tech - go read about its features. I can't wait for it to become stable/mainstream; sadly that will probably be another year or so. Filesystems need a lot of testing before production use.
Have I said I really like the features of btrfs (and ZFS) yet? If I had to write out the features of my dream filesystem, these would constitute a big part.