Manic Digger, a C# open source clone of Minecraft and Ace of Spades, is also getting a WebGL version.

http://manicdigger.sourceforge.net/ - click "development news"

I make it with Script# (C# to JS converter), WebGL, and WebSockets. Both desktop OpenTK version and WebGL version can be compiled from common source.

But it's missing 2 weeks of work to finish the port.