Geomena is an open geo database of WiFi access points meant to be used for geolocation. The database is as open as Wikipedia, editable and downloadable by anyone to use however they want. The API provides a way to be able to add data programmatically. It will enable applications that sniff WiFi and combine with location (either grabbed via GPS, address, or other methods).
Twitter and Facebook are often lauded as shining examples of what a platform does for your business. And for good reason. They have very successful developer programs. But they are also extremely popular services on their own. A developer may not build where there is not the foundation of a loyal user base. But even that has exceptions.