Stig Database: "Stig is a new open source, non-relational, distributed graph database being developed here at Tagged.
Our goal is to make it easy for programmers to store and access large amounts of connected data in a way that keeps consistency, while still being fast and scalable. Designed for planetary-scale, with real-time social applications and web developers in mind, Stig is the ideal database for large social networks, real-time services, and cloud applications."