mxGraph is a fully client side JavaScript diagramming library that uses SVG and HTML for rendering. It is the underlying technology that powers the drawing functionality that you see in https://www.draw.io.
mxGraph supports IE 9+, Chrome 30+, Firefox 31+, Safari versions actively patched by Apple (6.2.x, 7.1.x, 8.0.x and 9.x at time of writing), Opera 20+, Native Android browser 5.x+, the default browser in the current and previous major iOS versions (e.g. 9.x and 8.x) and Edge 20+.
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, https://www.jgraph.com/mxlicense.html. The mxGraph license is for commercial use, you can find the pricing at https://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, https://jgraph.github.io/mxgraph/. The key resources are the JavaScript user manual, the JavaScript examples and the JavaScript API specificiation.
If you are evaluating mxGraph commercially, please contact us via https://www.jgraph.com/contact.html and we'll arrange support during your evaluation.