Hi Muhammad Saqib,
Thank you for using our services.
Sitefinity is built making extensive use of the Telerik RadControls for ASP.NET AJAX. We also distribute the Telerik.Web.UI.dll with Sitefinity which allows you to use all controls from the suite in your Sitefinity website. Note that the controls can be used only within your Sitefinity website. You can use the RadControls to build your own functionality.
If you wish to use the RadControls for ASP.NET AJAX on another project you would have to purchase a license for them.
If you have more questions, feel free to contact us.
All the best,
the Telerik team