You'll remember Twitter Bootstrap, a toolkit by Twitter for kickstarting CSS development and creating beautiful interfaces easily.
jQuery UI Bootstrap is a jQuery UI theme that is inspired from Twitter's project and brings the slickness of it to jQuery UI widgets.
Using the theme, it is not only possible to use the Bootstrap-themed widgets but also work with Twitter Bootstrap side-by-side without issues.
You can also read more about the motivation behind the project on the developer's web page announcing the jQuery UI Bootstrap.
Compatibility: All Major Browsers