Nostr is the protocol and there's a bunch of clients. Uses pub/private keys and is easier to get started imo. Damus is a popular client for mobile, Snort and Iris are for desktop. You can attach any Lightning wallet you want. Hotbed of distributed computing innovation currently, lots of work to be done. But I'd argue engagement is up there and like Stacker, less like Twitter where it's essentially a no-fly zone without a blue check. Engagement also happens to be why people like Reddit, there's not an equal reason. Facebook/Meta was always more for your small circle, not casuals.