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).
And... it's free and open source: OpenUI5 is licensed under the Apache License, Version 2.0 - see LICENSE.txt
Check out our interactive control playground as well as a number of sample applications.
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.
You can also consume OpenUI5 using the UI5 Tooling. Get started here!
Alternatively, you can also download every OpenUI5 library individually via npm, for example: npm install @openui5/sap.ui.core @openui5/sap.m @openui5/themelib_sap_belize [...].
Preload packages for components and libraries can be built using the UI5 Tooling. See also: CLI guideline.
Try the Hello World, read the Developer Guide and refer to the API Reference. Use App Templates as a foundation for your developments (available in SAP Web IDE or here on GitHub). 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?