[buckbova]

Not C# but give kivy a try. Cross platform and in python. Great for student projects and those looking for open source alternatives.

http://kivy.org/docs/gettingstarted/intro.html

Other open-source alternatives are haxe and phonegap.

http://haxe.org/

http://phonegap.com/

Comparison site:

http://www.riaxe.com/blog/top-cross-platform-mobile-developm...