RazorControl is an experiment that lets you use the Razor ViewEngine from Microsoft directly in Umbraco templates. The implementation might change and should in the current state be treated as nothing but an experiment!
If the experiment becomes a staple succes it could be seen as a serious alternative to XSLT (that's the design goal!).
It stands on the shoulders of the brilliant work with wrapping Razor done by Matthew Abbott (http://www.fidelitydesign.net/?p=239) and BuildStarted (http://buildstarted.com/2010/11/02/razor-without-mvc-part-ii). Not to mention the work by the Razor team at Microsoft.