ffuent.es is a Fediverse instance that uses the ActivityPub protocol. In other words, users at this host can communicate with people that use software like Mastodon, Pleroma, Friendica, etc. all around the world.
This server runs the snac software and there is no automatic sign-up process.
I put muxleq https://github.com/howerj/muxleq (A multiplexed subleq interpreter) at #SDF among the web version of Starting Forth. With that among the functions to simplify fractions and lcm/gcd borrowed from "Introducción a Forth" I'm mostly covered for my small needs.