Pleroma is a microblogging server software that can federate (= exchange messages with) other servers that support ActivityPub. What that means is that you can host a server for yourself or your friends and stay in control of your online identity, but still exchange messages with people on larger servers. Pleroma will federate with all servers that implement ActivityPub, like Friendica, GNU Social, Hubzilla, Mastodon, Misskey, Peertube, and Pixelfed. Pleroma is written in Elixir and uses PostgresSQL for data storage. It’s efficient enough to be ran on low-power devices like Raspberry Pi (though we wouldn’t recommend storing the database on the internal SD card 😉 but can scale well when ran on more powerful hardware (albeit only single-node for now).