It was originally named JGraph through versions 1-5, this technically is version 6, but we changed the name to reflect the fact that the entire codebase and API was rewritten from scratch.
JGraphX provides functionality for visualisation and interaction with node-edge graphs (not charts). Example applications that you might write with it are a workflow editor, an organisational chart, a business process modelling tool, a UML tool, an electronic circuit diagrammer, network/telecoms visualisation (you get the idea, things with nodes and edges that connect those nodes, a mathematical graph).
JGraphX also includes functionality like XML stencils support, various import/export and layouting (automatically node/edge positioning).
There is a user manual http://jgraph.github.com/mxgraph/docs/manual_javavis.html that explains the basic architecture.
There are various examples, https://github.com/jgraph/jgraphx/tree/master/examples/com/mxgraph/examples/swing, from the usual HelloWorld to a more complete application example called GraphEditor.
There's also the API specifications at http://jgraph.github.com/mxgraph/java/docs/index.html
There is a 'jgraphx' tag on Stackoverflow - http://stackoverflow.com/questions/tagged/jgraphx, but please ensure you understand the SO FAQ and posting guidelines prior to posting. To post on SO you must 1) have a question , 2) that question be programming related and 3) use the 'jgraphx' tag. If it's not a programming question, post on our Google+ stream instead - https://plus.google.com/b/114366056917507510100/114366056917507510100/posts.