I am not sure exactly the best way to describe what keybase is/does.
They are a verification/tracking tool for usernames/accounts, they let you verify cryptographically that for example, I “rdyoung” am also in control of the username rdyoung on reddit, or the twitter account I set up for csc.
They are currently in alpha testing and I have 8 invites to handout if anyone wants them.
If anyone would like an invite, please post an email address here, or via pm and I will get one to you.
You can view my profile @ https://keybase.io/rdyoung