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They've got a whole process to joining fully, but it's explained on their discord channel. Their coolest thing, in my opinion, is their post promotion section- you have to upvote and comment on two other people's posts before each of your own you post (which you can only do once per day). It's a super handy model that fosters a ton of community interaction.

I'm actually surprised someone in the crypto space has not modeled a new social media platform that recognizes and rewards real user engagement and quality content via an underlying blockchain as its foundational basis. Is this something that anyone is doing? I am not aware of any such initiative outside of Steemit.

Up until now social media hasn't been a particular priority of blockchain technology- everyone's just been focused on the cryptocurrency aspect of it. If anything, cryptocurrency is actually holding back the development of blockchain as a viable technology, because everyone just wants to be the next big coin and make a bunch of money, and it's reducing diversification. (Not to mention outside interest in it.)

And yeah, I'm only aware of a few other blockchain based social media platforms- a couple of steemit clones in other languages and a terrible ethereum based one. There's really no other interesting, original blockchain social media networks. (Not that the world necessarily is into many more social media networks- it's proven pretty intolerant to new ones recently, and steemit only made it because it has its own unusual niche.)