I can't speak much about the technical stack, although I would probably write it in Python and or TypeScript because that is easiest for me, or in something exo

I can't speak much about the technical stack, although I would probably write it in Python and or TypeScript because that is easiest for me, or in something exotic like Nim for fun. If decentralized, I would think about a clause in the license that mandates some kind of federation. Although, it seems like the ability to not federate with certain instances is seen as a selling point for some Mastodon users. Most importantly, I would not try to build a Twitter clone. Twitter is often "yelling into the void" aka write-only, and when you get something back it is often aggrivating. Sure, you can also have great exchanges and meet nice people, but all in all it is just not so pleasant. What I would go for instead is a clone of early Facebook or MySpace. You have a profile page, you can present yourself as you like. You have statusses but no global feed by default. People can send you private messages, but they can also interact in some fashion with your profile. A social network, instead of social media. One thing I'd like to experiment with is derived identities. Say you want to participate in a community (forum, group chat) with similar people. You want to use a pseudonym, but the community wants some assurance that you are really a teenager, or a woman, or a technology expert, or whatever. Your main profile would "prove" this, but you don't want to disclose your identity. So you create a new account, and the system would vouch that the new account is e.g. from a woman older than 21 with an account in good standing, but disclose nothing more. I think I can work out a cryptographic scheme so that even the server cannot connect the two accounts, but everybody can verify the proof... but it is tricky. Looking forward to verified celebrites and government members with alt-accounts posting controversial stuff under pseudonyms ;-) ... OK maybe not, when I think about it.