FreeSG ("Free" as in "Free software" and "Free of bloat") is an compact, general-purpose, open-source scene-graph library. It implements a generic, extensible object/scene representation, designed to simplify such tasks as real-time rendering and geometrical queries. One feature which distinguishes FreeSG from the variety of scene-graph libraries available is its ability to solve systems of logical (geometrical) constraints such as angles and distances, in order to define the relationship between elements of a scene, in a powerful and unambiguous way.