(btw, "hiding capabilities of a general purpose database behind a narrow API" is one of the motivating factors behind REST service design. It's modularity by another name, with its own costs and benefits. If I had to do this inside my service, I'd think of it as a code smell.)
Ceejbot's mastodon instance. This is an overprovisioned, personally-run instance running on AWS. I welcome friends to create accounts here. I intend to run it as long as people are using it.