Hammer is very much like having your entire filesystem in git.

https://www.dragonflybsd.org/hammer/

"HAMMER retains a fine-grained history. The state of the filesystem can be accessed live on 30-60 second boundaries without having to make explicit snapshots, up to a configurable fine-grained retention time.

A convenient undo command is provided for single-file history, diffs, and extractions. Snapshots may be used to access entire directory trees."

edit:

Just now, 10 minutes after posting this, I regretted deleting a file (cabal.sandbox.config) and was able to restore it:

    > rm cabal.sandbox.config // oops
    > undo -i cabal.sandbox.config
    cabal.sandbox.config: ITERATE ENTIRE HISTORY
	    0x000000010bf2e940 17-Apr-2015 06:50:48
	    0x0000000112282990 18-Apr-2015 20:36:53
    > undo -t 0x0000000112282990 -o cabal.sandbox.config cabal.sandbox.config

That's seriously cool. What's the stability/speed like?

Looks quite good: https://www.dragonflybsd.org/performance/

I'm not really sure how to benchmark it myself, those are from 2012 and I'm sure things have improved since then.

On Plan 9, the Fossil file system, almost invariably paired with the Venti archival storage server, do precisely that: http://man.cat-v.org/plan_9/4/fossil

You could replace rm with an alias to small script, e.g. mv to ~/.trash rather than deleting the target. The trash can be auto-cleared based on space constraints or after a certain time.

libtrash does this by hooking libc so it works for anything that deletes files (unless it's statically compiled...) - it's been around for ages. http://pages.stern.nyu.edu/~marriaga/software/libtrash/

Sadly, the local system is only a small part of what you can screw up. It becomes the undo-email problem pretty quickly.

ZFS

Nice try.

ZFS is production ready. Use FreeBSD!