Keyoxide is an open-source platform for creating and verifying "distributed online identities" using cryptographic signatures. It allows a person to provably link their online identities together across multiple platforms using OpenPGP and bidirectional linking.
The Keybase web app can be self-hosted, and there is a CLI tool which can be run locally. Because identity claims are made on the user's own OpenPGP keys or via signed plain-text documents, the platform is stateless and does not store any user data.
Keyoxide supports the following IndieWeb building blocks: