I honestly hate what corpos are doing lately with applications and platforms, prioritizing quantity and adding unnecessary crap and bloat that nobody asked for (cough cough, AI and abruptly changing their UIs making them more annoying to use than before) rather than improving their services (and then they wonder why they're losing users and why they're getting the criticism they honestly deserve). In other words, enshittificating something that always worked fine at first place just cuz $$$$$$$$$$$$$$$$$$ talks first than users.
I started using alternative platforms since 2021, mostly chat ones as I was tired of Discord and I wanted to move to another similar chat platform/app. Back in those days the only similar project was Revolt (now Stoat) but nowadays I just use Nerimity but only for talk with my only friend on DMs as I never saw a server that got my interest yet on the Discovery tab (too much boring mainstream memes, games and filler servers).
As for "social" media alternatives, aghhh. I used to use Mastodon back in 2021 and I also used to have my own self-hosted pseudo-Mastodon instance (actually a GoToSocial instance) during 2024 but they always end up boring me so fast after a few days and I end up deleting my accounts as I no longer like using "social" media platforms these days (and yeah I write "social" with quotes cuz it doesn't have anything of social these days as most of them are nowadays a cesspool of toxicity and similar, just read this: https://ctrl-c.club/~lars_the_bear/its_not_me_its_you.html).
Nowadays I just prefer going back to classic weblogs and personal homepages (retro-web/indie web/web revival) even if no one cares about them (and actually I don't give a heck if no one is going to see those websites and if I don't receive "attention", I don't want to be famous anyway). It gives me that sense of calm, creativity with web design (instead of being limited to only change a description and a banner) and freedom, instead of the chaos and how noisy are those platforms nowadays.
Overall I just prefer forums to anything though, and forums are considered alternative platforms at this point too!
Same too. I born using forums/message boards in all the time I've been using Internet and I like threaded discussions rather than real-time chatting as it makes a conversation more paused and it makes you to take time of what you're going to write instead of chat apps which prioritize rushing. And also because info/content on forums are usually public accessible instead of this stupid nonsense trend I'm seeing lately of closing all important information, files and even support on a single Discord server. And yeah I know that latter is because mostly of how much damage AI scraping has been doing with some small and even large forums these days that most of them had to close or shut down, but heck man that's not an excuse, just use Cloudflare's bot protection, install something like Anubis or go-away in your server or just make manual or invite-only signups. Moving everything to Discord isn't a solution and it only generates more inconveniences for other users that doesn't use it or doesn't want to create a Discord account (for obvious reasons).