Mastodon has been around since 2016 and has 804k MAU.
The platform has 57 third party apps.
The platform is decentralized and has community ran servers.
I think it’s much more difficult to find people to follow. I personally struggle a lot, and will likely either gave up the micro-blogging system or try another platform. It was great on Twitter before Musk bought it, but since I left, I have yet to find an alternative.