Skeltrack is a Free and Open Source Software library for tracking the human skeleton joints from depth images.
It is implemented with GLib and uses plain mathematics to detect the human skeleton and although it does not use any database, it was inspired by Andreas Baak's paper: A Data-Driven Approach for Real-Time Full Body Pose Reconstruction from a Depth Camera
Although it is device agnostic, a common way of using Skeltrack is to use it together with a Kinect device, for which we recommend the GFreenct library.
Checking out the examples/test-kinect example app is a good start in order to learn how to use Skeltrack.
You can find the documentation for Skeltrack here: http://people.igalia.com/jrocha/skeltrack/doc/latest/