Just like passports for real life identities, Keyoxide can be used to verify the online identity of people to make sure one is interacting with whom they are supposed to be and not imposters. Unlike real life passports, Keyoxide works with online identities or "personas", meaning these identities can be anonymous and one can have multiple separate personas to protect their privacy, both online and in real life.
Keyoxide allows you to prove "ownership" or rather "hold" of accounts on websites, domain names, instant messaging, etc., regardless of your username. You create, or use and existing, cryptographic signature (or OpenPGP key) which acts as your digital passport to link to the various services. I used my existing key with this, and just added the notation claims per service, with my proof placed in the profile of each service I control.
Whilst Keybase is still alive, since its takeover by Zoom, it has been a lot quieter. Keyoxide also allows you to self-host the service, and seems to have a lot of flexibility for the services it links to.
That said, I got a good 10 of my various services linked and verified, except I've had endless issues to get my IRC and XMPP accounts verified.
Modern and secure platform to manage a decentralized identity based on cryptographic keys