We've waited a little to properly announce this, just to make sure everything was in place, but we've now opened up our source code. The 'repository' (the collection of source code) is now public on Github, here:
The application is written in Java, with the Spring framework. It's a modular application, so the core objects are in, well, grassroot-core; the services that use them are in, well, grassroot-services; and the pieces that respond to USSD calls and handle the views for the web are in grassroot-webapp (i.e., USSD is in there too).
The license is New BSD, also called BSD 3-clause. That means anyone can clone the source code or the application itself (hence 'open source'), but have to (a) make it open themselves, and (b) cannot claim to be endorsed by us or any other contributor, or use our name in any other way (unless we give permission of course). It also means we give no warranty and cannot be held liable for anything done with the software. More here, for the interested.
Last, we'd love contributions if people would like to help out. Since we're a small team and the code base is still pretty raw, we'd ask that you get in touch with us first (firstname.lastname@example.org) so we can talk about what would make sense, and know what you're working on.