Just a couple of clarify notes:
1) As noted earlier, a Geni 'project' is not like a technical/business project. A Geni "Project" is simply a software construct to allow a 'connection' or 'collection' of information to be "tied together". In some ways it is similar to a "profile" for a person (in the genealogical sense that it is used on Geni) that "ties together" a variety of data & links to other entities.
'Membership' in a project is to enable collaboration on the "items" associated with that project.
All of that, in a theoretical sense, has nothing to do with the "title" of the Project.
So, joining "The Geni API" project means (solely) that you can help contribute to, add to, and update the 'materials' / 'items' associated with that project.
I can understand the implication that it would have to do with the actual API code, though!
2) Geni is not Open Source; the API is something Geni has 'exposed' to enable programmatic interfaces.
One of the uses of this particular 'Geni Project', though, is as a means for the Geni API developers/maintainers to see what the users of the API have to say & how they might be using it.
3) There are a number of users here who have years of experience working with the Geni API ; my knowledge is more 'theoretical', rather than as a hands-on programming user (at this point). <smile>