Well, I've made something for a very niche group of people.

I made a really small simple tumblr clone social network, and a few months ago I was able to kind of bugily conect it with mastodon.

https://app.wafrn.net

It has 400 registred users, of wich in the last month 20 have posted.

https://app.wafrn.net/.well-known/nodeinfo/2.0

This endpoint I added it not too long ago to be more "friendly" towards other nodes