Name: NeoCities
Homepage: https://neocities.org/
Short description: "Neocities is a commercial web hosting service for static pages. The service's expressed goal is to revive the support of free web hosting of the now-defunct GeoCities." WikiPedia
Optional API documentation URL: https://neocities.org/api

You can do something similar to how it works with Reddit. The user makes a post under their profile and Keyoxide looks for that comment.

For example, the user posts a comment under their own profile page that says something like "OpenGPG key: FINGERPRINT". The notation would be something like "proof@ariadne.id=https://neocities.org/site/USERNAME?event_id=COMMENT_ID"

    wandering_girl Great suggestion!

    I have just proposed a generic method which would allow verification of any personal site where the user controls the HTML content. Do you think this would (if implemented) cover your use case for Neocities, or do you think it would still be useful to implement a Neocities-specific proof method?

        Thanks for the suggestion, @wandering_girl and indeed @caesar solution for any personal website should work with NeoCities as well!