OpenSolaris is really Open: Dtrace in MacOS.
By Franz Haberhauer on Aug 15, 2006
Update Aug. 22: Pawel Dawidek is porting ZFS, Suns next generation filesystem, to FreeBSD and has already made good progress after just 10 days. There is also the ZFS on FUSE/Linux project porting ZFS to Linux in userspace. This approach can be used to get around the license restrictions the GPL enforces for the Linux kernel.
I will give a talk on ZFS at the at the german Linuxworld Conference in November.