GNU social was a spin off, later merging with StatusNet and later Mastodon was a rewrite of GNU social in Rails.
https://git.savannah.gnu.org/cgit/librefm.git/tree/gnufm_ins...
I’m no longer involved with the GNU project so the site is in a weird state where the GNU docs are stuck in time. I do need to do a better job of pointing people to what’s out there though. I am considering a rewrite in modern PHP.
GNU social was a spin off, later merging with StatusNet and later Mastodon was a rewrite of GNU social in Rails.