n0tice is a simple location based public notice board system. It's completely open and unfiltered, and allows users to post any sort of notice they want, tagged with their location, and lets them read notices near them, sorted by distance. Quite a simple little idea, and if it gets a user base, it could end up being quite useful. Although first designed for iPhone, the n0tice API was quickly released to allow integration into other programs, including desktop apps.
What would it mean to have a stripped down social network that was also secure? It would look like Tuenti, the social network out of Spain. To give an example of how seriously they take security, the Tuenti API is closed because "of our efforts to be the most private, secure social network on the market..." But if you play nice, they can make exceptions for commercial apps and games they have tested.