Like #Gravatar, it's a way for users to change their profile pic/ avatar images in one place and have it propogate across other servies they use. But unlike Gravatar, it's decentralized and not controlled by Automattic. It is fully #FreeCode and compatible with #OpenID though.
The social network of the future: No ads, no corporate surveillance, ethical design, and decentralization! Own your data with Mastodon!