The ZFS filesystem which was being used by developers at Apple for a possible future update to the Snow Leopard OS or future OS X systems has been stopped indefinitely according to an official statement by MacOS Forge.
The statement couldn't be anymore clear:
The ZFS project has been discontinued. The mailing list and repository will also be removed shortly.While many rumors about the reasons for the work stop have surfaced, there's speculation that the purchase of Sun by Oracle added to those issues. Oracle owns their own filesystem (BTRFS) which is still under development and which would have competed against the ZFS system. While ZFS has also faced patent issues that could have potentially led to lawsuits and other development issues down the road. [AppleInsider]