DragonFly caught my interest a while ago with Hammer FS, which by all accounts is pretty astonishing considering how small its development team is.
However, last time I installed it in a VM it didn't seem to have a huge amount of software available to it without compilation - it used the same pkgsrc ports as NetBSD, which are fairly extensive, but there seemed to be a lot of build failures or something... Not too sure, I didn't dig into it in detail, but many for me key applications were missing (and I wasn't really interested in compiling everything).
The most recent release has switched over to pkgng from FreeBSD for its primary package management, and seems to have plugged this gap.
And Hammer is really, really clever. You can configure a retention policy, so for example all files / directories / entire filesystems can be accessed as they were at any point in the last few months (with something like 30 second to 1 minute granularity), or files can be accessed by specific revisions. Obviously this takes up space, but it isn't egregiously heavy - and its RAM / CPU load is nothing like ZFS's. It's reckoned to work reasonably well on anything with more than 512M of RAM and 50G drive space.
Worth looking at.