No its their service pack stuff. Tiger, current version, is 10.4. The current release is 10.4.8. It's not decimal though, the dots are just there are dividers. Periodically they fix security problems or little bugs and release them, and every few months they come out with a more complete fix list of the core OS, in the form of 10.4.9 or whatever.
ZFS is the zettabyte filesystem, developed by Sun. It's a hot new thing, and not many people are using it. But it has some amazing features that make it great (plus it's open source).
- storage pool. Unlike current filesystems, you can connect another drive (internal or external, whatever), and tell it to join the storage pool. The filesystem will now span that drive too, so you instantly get more room to store your stuff on. No transferring stuff across or anything like that, it's all automatic.
- compression. you get great compression on your stuff automatically -- it's totaly on the fly.
- integrity checking. with other filesystems your data is stored there and its as simple as that. with ZFS, it checks to make sure that your data isn't corrupted, and if it is it can automatically fix it for you
- snapshots. this is what gave hints to ZFS from Apple initially -- their 'time machine' system is perfect for this. say you have a word document, and change one sentence then save it again. it can be made to make snapshots of your files, so that the original file is stored, plus another one with the new sentance and where it's supposed to go. if you try and open this new 'snapshot', it'll automatically grab the old file, substitute the new sentence in, and display it for you. because of the compression, your disk isn't always full either.
in short, lots of great features, but there are plenty of articles on it. as a RAID user, you may be very interested in it.