I'm not seeing much mention in this thread of the cryptographically-linked identities feature of Keybase, i.e. where you can link your Website, Twitter, Reddit, HN, etc.

As far as I know, that was Keybase's initial offering, which they then built on top of to create a full suite of applications.

Although to play the Devil's advocate - while the feature is cool and implemented nicely, I doubt that many people actually use it beyond the novelty factor.