I thought this was a repost but I was thinking of dolt which has similar capabilities but a different approach. As in https://news.ycombinator.com/item?id=38109880

Neon is basically this same idea: postgres on a copy-on-write file system.

These aren't really "branches" though, they're hard forks. You can't merge them back after making changes. Dolt is still the only SQL database with branch and merge.