This morning at MVP Summit, Scott Hunter just announced a new open source project fromappendTo called Juice UI. Juice UI is a collection of Web Forms components which make it incredibly easy to leverage jQuery UI widgets in ASP.NET Web Forms applications. You can start using it right away by adding the JuiceUI NuGet package to your app, and you're welcome to go nuts with the source, which is dual licensed under MIT and GPL.
Basically this is a version of the AjaxControlToolkit powered by jQuery and jQueryUI.
An important thing to remember is that often the worst abuse of toolkits like this came alongside our good friend the UpdatePanel. If you take that out of the mix then things might not be so bad, however I often saw them go hand in hand together.
Plus, they do look pretty neat:
Link: Juice UI: Open source ASP.NET Web Forms components for jQuery UI widgets