Under your 'Account settings', go to 'Authorizing applications & sites' in the first section (Security).

curious. i had "localhost" listed there. what does that mean? i revoked access and am still logged in to gmail.

(i know what localhost means, in that it is the name associated with 127.0.0.1, but how is it a "connected site, app or service"?)

Perhaps someone showed you a web app demo on their desktop or laptop (and said app was installed on the same machine) and you used Google to sign in.