What's it for?
I post something and my followers see it. That's the rough idea behind the pump.

There's an API defined in the API.md file. It uses activitystrea.ms JSON as the main data and command format.

You can post almost anything that can be represented with activity streams -- short or long text, bookmarks, images, video, audio, events, geo checkins. You can follow friends, create lists of people, and so on.

The software is useful for at least these scenarios:

Mobile-first social networking
Activity stream functionality for an existing app
Experimenting with social software
It also comes with a web UI.