Ligature is a libre (free and open source, MPL-2.0 licensed) knowledge graph that focuses on pragmatism, portability, and simplicity. It is currently under heavy design and development, and not ready for real world use, but experimentation and feedback are encouraged and much welcomed.
Below are some resources to see where things are.
Work on Ligature is spread out over a number of git repositories. Below is a list of them.
This website makes use of the follow projects and libraries (probably a few I'm forgetting)