Bonfire is a Fediverse project that aims to store your social data on a physical device that you own (for example a Raspberry Pi running Bonfire software). It will also operate offline if preferred.
It's still in development, but you can follow the project at:
The new official website is at https://bonfirenetworks.org
(It was previously known as CommonsPub.)
A newer server operated by the Mastodon gGmbH non-profit