mxGraph is a fully client side JavaScript diagramming library. It is the underlying technology that powers the drawing functionality that you see in https://www.draw.io.
We started developing mxGraph in 2005 when Internet Explorer 6 and Firefox 1.5 were the latest browsers, thus we still support all browsers back this far for IE and FF, as well as most Opera, Chrome and Safari versions. mxGraph supports iOS and Android touch events.
mxGraph uses the vector drawing language native to the browser being used, VML for IE 8- and SVG for more modern browsers.
mxGraph uses no third-party software, it requires no plugins and can be integrated in virtually any framework. Also provided is server-side functionality in Java and .NET for persistence (open and save) functionality, as well as server-side image generation.
mxGraph is licensed under the mxGraph license, http://www.jgraph.com/mxlicense.html. The mxGraph license is for commercial use, you can find the pricing at http://www.jgraph.com/purchase.html.
In the root folder there is an index.html file that contains links to all resources. You can view the documentation online on the Github pages branch, http://jgraph.github.com/mxgraph. The key resources are the JavaScript user manual, the JavaScript examples and the JavaScript API specificiation.