I stumbled across Coolite the other day, and thought it looked cool (excuse the pun). In case you don't know, Coolite is a new project that aims to wrap the ExtJS Ajax controls in such a way that they can be used with ASP.NET in a similar fashion to other ASP.NET controls.
I thought it might be fun to see if Coolite could run in Mono, and so far it's looking good!
Getting it working was easy. I just added the DLL reference and copied some code over from the Coolite site samples. Then hit RUN and it worked :) Actually, there is one bug so I had to swipe out the ClientEvents tag on one of the panels (which is just supposed to call some JavaScript).
On a tangent, I've only been playing around with Mono and MonoDevelop for a few days, I'll be blogging about that separately soon :) So far the experience is a good one.