Consider joining the Fediverse, a federated (which means that user-run servers can talk to one another) social media platform. You probably know it from all of the headlines that Mastodon's been getting, but it's a lot broader (and better) than what Mastodon's press coverage has implied it is.

If you want to self-host, a libre server with more features than Mastodon can be ran on a Raspberry Pi: https://pleroma.social/

If you have some really old hardware, a server running Honk can run on something with 30MB of RAM and an old hard drive, though it's (much) lighter on the feature end, too: https://flak.tedunangst.com/post/honking-for-fun-and-profit

Want an Instagram alternative instead of/to complement a Twitter alternative? Try Pixelfed: https://pixelfed.org/

Want a YouTube alternative? It's got one of those, too! Check out PeerTube; with over 100,000 videos uploaded so far and a better interface than YouTube's, it's already a really viable contender: https://joinpeertube.org/

If you don't want to self-host, there are five thousand instances you can join, with a collective amount of users nearing 5,000,000! Proof of those numbers, and a list of instances: https://fediverse.network/

If you like the sound of this, find an instance with a moderation policy you respect (they range from "Do nothing illegal, please!" to "Don't do something we dislike or you'll be banned," so this step is important), and register! It's much comfier using smaller ones, and knowing the person who's running your instance and vice-versa makes your experience a lot better, so try using a smaller instance!

A lot of HN users are already on it. A few even volunteered their handles in the last thread:

https://news.ycombinator.com/item?id=16741116