ZFS is an example of one that's recognizable, you can bolt it onto linux and it (now) works quite well, but it was integrated much more into Solaris.
There are also Unix platforms that fully support hot-swappable just about everything, which you CAN do with Linux but it's not as simple.
Most of that stuff is gone by the wayside now, Linux is "good enough".
It won't surprise me if one of these days Oracle decides that Canonical is a ripe lawsuit target over ZFS.
It's similar to the "polish" available on macOS or Windows, Linux has all the pieces but you have to assemble them yourselves, even today.
Because there's a moderate change that it goes against them.
I hope btrfs becomes quite stable and usable.
That whole CDDL/GPL incompatibility is BS.
(speaking as the guy who wrote the scripts to change all the license text, though the actual relicensing was due to a lot of work on my boss's part.)
And canonical includes ZFS, and i think they have more lawyers then you and me.
Do you really think they would take that risk especially with oracle to include ZFS (that is not even their main fs)?
Have some commonsense.