OpenUI5. Build Once. Run on any device.
OpenUI5 lets you build enterprise-ready web applications, responsive to all devices, running on almost any browser of your choice. It’s based on JavaScript, using jQuery as its foundation and follows web standards. It eases your development with a client-side HTML5 rendering library including a rich set of controls and supports data binding to different data models (JSON, XML and OData).
Check out our interactive control playground as well as a number of sample applications
It's free. Go to the download page and get the complete UI5 runtime and the UI5 SDK containing the documentation and many example apps as well as the complete runtime.
Try the Hello World, read the Developer Guide and refer to the API Reference. Check out the SCN Forum and stackoverflow (use the tag "sapui5") to discuss code-related problems and questions.
You can get the sources and build UI5 on your own, please check the documentation for the UI5 development setup. You might then want to understand how control libraries are structured and controls are developed. Maybe there's a bug you could analyze and fix?