We're less than a week away from Twitter changing their rules for third party apps, changes that will fundamentally change how useful those apps will continue to be, and that can only mean one thing: it's time for Twitter alternatives to have their place in the sun!
The two main ones I see are Micro.blog and Mastodon. Micro.blog is the more popular one right now, it seems, but Mastodon has its fair share of loyal fans. I personally have accounts with both other services, but I don't really use them reliably. Mastodon because I can't find anyone on there, and Micro.blog because I don't like any of the iOS apps available for it.
I don't expect to move over to either of these as my main social network, but Twitter's latest waves of jack-assery has kickstarted the conversation again. There are a few problems with these other services, but the main thing is that they just haven't managed to get enough people to stick around and use them for long. People tend to try them and bounce off them pretty quickly. I know I have bounced off each of them numerous times.
Twitter's key advantage for me is that it just feels like the place everyone is talking. Basically everyone you want to hear from, whether they be celebrities, athletes, politicians, actors, writers, or regular old people, they're almost certainly on Twitter. Not only are they there, but they're active and use it as a one-stop-shop for talking about everything they're doing. If you're not on Twitter, you're cutting out a main place things are announced and talked about.
With these other services, I don't feel like I'm missing out on anything. Yeah, there's probably a lot of good people there, but I don't know those people, and it's almost impossible to figure out who is worth following. Again, since almost no one is there, you can't just type in someone's name and expect them to come up as a search result.
This leads you to following random accounts who you think may be interesting, but turn out to not be as interesting as you'd hoped. Or you follow the 5 people from Twitter you know on there and then realize they tweet more than they post at this other place, and anything important will go on Twitter too, so you don't see value there either.
App.Net was, I think, the closest we've come to a good Twitter alternative, and it came out back in 2012. It did basically everything Twitter did, but nicer. It had a decent web experience and a great selection of third party apps up and running within weeks of launch. And while it was a paid service (and maybe therefore doomed from the start), tons of people in the tech community went there and were having lively discussions. My App.Net feed was a joy to browse, and most of my Twitter friends were there. Oh yeah, and it was an app platform that let some devs build off their back end in interesting ways.
As mentioned, App.Net was doomed and just 2 years later it announced it was shutting down, but I still think it was the closest we've come to something being a real alternative to Twitter. Based on its short tenure, it certainly wasn't big as it needed to be, but personally I still loved it.
It's incredibly hard, and involves a good deal of luck, but if something is going to be a real Twitter successor/alternative, it needs to first and foremost find a way to get a critical mass of people using it. That can be a critical mass of a Twitter sub-culture, but it needs to be some group that moves in mass. App.Net get "Tech Twitter" to move, but it failed to get more than that (or to make them actually leave Twitter), but I don't see that happening with Micro.Blog or Mastodon yet. I don't know how you do that, but I think that's how you get the momentum.
I'd be remiss to not mention Slack or Discord here as well. Those services are good, but they are too insular to be a real threat to Twitter. You have to know someone on the inside to get in yourself, and there are so many versions/channels/servers for you to join it's hard to keep them all straight. They can be good for you and a couple dozen (hundred) of friends to stay in touch, but it's not great for a Twitter-style experience.