What are Keybase teams?
A Keybase team is a group of people who can communicate with end-to-end cryptography. This means
the team's chats and files cannot be read by anyone outside the team, not even someone who
breaks into Keybase's servers.
Membership/role changes
are entered into a chain of signatures which (1) cannot be altered by a malicious person
outside the team, and (2) must be signed by a team admin, as defined by previous links in the
chain.
Open communities also benefit from Keybase, even if encryption isn't the goal, since data is
cryptographically signed.
Here are the crypto docs for the academics among us.