Kendo UI Core is an open source version of the Kendo UI library that includes core UI widgets, charts, and frameworks for building websites and mobile apps. It contains 24 widgets, core framework components, mobile widgets, and mobile features. Some key differences between Kendo UI Core and the commercial version are that Core has restrictive open source licensing and only includes major releases without commercial support. Kendo UI Core can be obtained from GitHub, NuGet, direct download, or a CDN and includes demo applications for the web framework, widgets, and mobile widgets.