Microsoft XNA is a set of tools with a managed runtime environment provided by Microsoft that facilitates video game development and management. XNA attempts to free game developers from writing "repetitive boilerplate code" and to bring different aspects of game production into a single system.
While not an engine it is an extremely useful frameworkt that saves me a LOT of time when making games... just beware that is made by Microsoft, so unless you use unoffical porting software you are stuck with releasing your games on MS devices