Tomorrow the 21st I will be participating on the Evolution E-Plugin hackfest. The hackfest will take place in the #evolution IRC channel on irc.gnome.org.
We will be learning the E-Plugin interface that Michael Zucchi designed for Evolution. Now Evolution 2.x can be extended with user code to implement your favorite missing feature or your favorite aberration.
Plugins are typically built with C but there is a Mono interface so any Mono supported language can be used to extend evolution.
This blog entry has some demos of the E-Plugin from August, it will give you a few ideas of what can be done.
Mark Crichton's Mozilla# for Windows
Mark has Gecko-sharp running on Windows (this is the Gecko binding for Gtk# running on Windows).
Gecko# on Windows.