RIOT is a fed-server chat with rooms.You make a profile on one of the hundred servers , and choose/create a room. For example DACNET-MAINN, or YOUR-OWN. The rooms are end-2-end encrypted and pretty secure (France gov will use Riot !). Being private and encrypted not even the server can see the dialogues. MASTODON-HALCYON is like twitter but on fed-servers. Here the dialogues are publicly viewable! So comply polite-customs and laws . Millions use today Mastodon on hundred of servers ww! It runs on Activity-pub.