Meta's Sapling source-code management system

Yeah, the up-streamed stuff from gvfs/scalar is also pretty vastly improved over what was in the old fork. sparse index/worktree/clones are way better than gvfs because you don't need to worry about some random program enumerating the git repo (including getting file sizes) and causing gvfs to download everything. I had both TortoiseGit and WinDirStat do this, it's quite annoying.

Something not in git uptream that I would love to see is a way to automatically symlink/junction git submodules (the ones in .git/modules) to some central area, scalar (the from git-for-windows) does seem to _somehow_ do this, I think using the alternates mechanism and a shim clone/fetch command but it's not super clean. I would be happy just getting modules pointing to exactly the same initial remote pointing somewhere common, it would at least make it harder to end up with 10 different copies of LLVM's repo on my machine.

Oh, another pretty easy win (on linux, at least, but perhaps on windows and mac with a compatibility shim) would be teaching git-checkout-index to use copy_file_range when available. The first "chunk" of the (unpacked) git object doesn't match the first "chunk" of the checked-out file so it's kinda filesystem specific if this works. And ofc on windows even if you have a compat shim almost nobody can use it because ReFS/btrfs/zfs are not widely used (I think those are all the CoW filesystems with windows implementations).