I have been using the AJAX Control Toolkit ever since it was released and have really liked it. Microsoft released it to Open Source and now they have turned it over management to DevExpress. Look for a new release in 2015.
Here is the blog post on the news: https://community.devexpress.com/blogs/aspnet/archive/2014/09/22/ajax-control-toolkit-devexpress-offer.aspx
dotNetTips.com 