This post was my first introduction to it too. Searching for "git.io" on github....

placatedmayhem on Jan 21, 2022 | parent | context | favorite | on: Git.io no longer accepts new URLs

This post was my first introduction to it too. Searching for "git.io" on github.com, including the quotes, returns a number of repositories using git.io links -- "2M+" if their search is to be believed.