Here's a little something that took a couple of hours to write, feedback is as always appreciated! As I've already been asked: this is all GDI based, no DirectX... Graphics for it would be appreciated!
Anyway, click here to run GravCave from my server, you need the dot net framework - available from windows update, or I expect it will run okay under mono. If you wish you can right click and save target as to your local machine - it's 40kb and will run from anywhere.
Another .NET game in the same vein is Chris Sells' Wahoo. This came about as I was curious why dot net based games weren't slowly appearing yet, so thought I'd see how difficult it was to code a game in: turns out with C# it's much easier than many other languages.
I assume when people realise that they CAN use DirectX with an app that is loaded directly from the net, they'll start using it.
UPDATE: Source code is available on this page on my sitePermalink