Probably didn't make it clear enough, it's repeatable so you'd use Twitter as the service and whatever password you usually use (master password), it'd come back with a hash and you use that as your Twitter password. Whenever you need your Twitter password, you repeat the process.
https://github.com/simontabor/pw - it's got node-webkit so there's a mac app in that repo and should also work on Windows + Linux nicely (this is simply to take it out of the browser where it's easy to lose tabs and put it in a clean, small window)
