In mathematics, graph theory is the study of graphs, which are mathematical structures used to model pairwise relations between objects. A graph in this context is made up of vertices, nodes, or points which are connected by edges, arcs, or lines. — Wikipedia

D3 Graph Theory is a project aimed at anyone who wants to learn graph theory. It provides quick and interactive introduction to the subject. The visuals used in the project makes it an effective learning tool.

And yes, it is an open-source project. Check the code at GitHub.