ZFS on windows: https://www.phoronix.com/scan.php?page=news_item&px=OpenZFS-...
That seems only slightly less scary than the btrfs on Windows project (which suggests disabling SecureBoot). At least it's from a ZFS contributor (while btrfs on Windows seems like a from-scratch rewrite, ie. all the bugs all over again).
From the comments here I take it people aren't actually using anything with features like snapshots/cow/compression on Windows :-/
Microsoft has somewhat ridiculous driver signing requirements. I become angry about this perhaps once every four months.