My good friend Torello Quercy has been working on creating OLPC activities using Mono.
He wrote a tutorial on creating Mono-based activities for the OLPC.
See his blog for screenshots of his own game and a port of Jordi Mas' GBrainy and how he Sugar-ified the apps:
GBrainy Sugarified on the OLPC.
Posted on 03 Jan 2008