It also:

- Doesn't need a phone number

- Has good multi-device support

There's also other fun stuff like Kbfs: https://keybase.io/docs/kbfs

I think of Keybase more as a cryptographic platform which can bundle devices and identities into a single package, see my "tree" for an example https://keybase.io/azag0/graph

It also provides crypto for files, both signing (public sharing, https://keybase.pub/azag0/) and encrypting (private sharing).

EDIT: And this short description doesn't really make Keybase justice. The whole project is much grander.

The chat is largely incidental to the actual use of keybase which is more of a convenient wrapper around key management and identity proofs. Signal doesn't allow you to take your key and sign or encrypt files without sending them through signal and doesn't interact with any other services.