Pleroma is light enough to run on a Raspberry Pi; its primary web interface is inspired by Twitter but it also includes the classic Mastodon interface at https:

Pleroma is light enough to run on a Raspberry Pi; its primary web interface is inspired by Twitter but it also includes the classic Mastodon interface at https://host/web https://host/web endpoint. It's very easy to set up and run. It's also compatible with anything that works with Mastodon via MastodonAPI (bots, desktop clients, mobile clients such as FediLab). Definitely the best ActivityPub software on the market!