Peas seems to be less feature complete. We use Heroku's logplex for storing the logs (something peas doesn't do yet, they do have a development branch that uses mongodb for that), and we also store the github repositories on the server, like Heroku does, while peas requires you to use a separate repository. We also work as a multi-tenant system (although admittedly, accounts need to be pre-seeded right now), while peas has no notion of users. I like tombh's work though, I just wanted to release my own system, since it predates peas.
tl;dr: Peas offers a few less features, but is more lightweight.