The core of the library revolves around different mouse interactions, namely drag and dropping, sorting, selecting, and resizing.
On top of the core interactions are built a number of reusable widgets, including accordions, date pickers, dialogs, sliders, table sorters, and tabs.
Finally, the library is finished off with a few effects that you can use to liven up your site, specifically magnifier and shadow.
In a crowded space jQuery really shines as the most simple & powerful library available. Take a look.