There are quite a few Dreamcast tech demo videos and images knocking around on the internet - from the Irimajiri 'floating head' and Tower of Babel videos to the less well-known Future City sequence (pictured below). It seems there is another one to now add to this list, but this one is quite interesting in that it is actually available to download and is fully playable: Defense Commander from Titanium Studios. I had never heard of it before seeing the video posted below, and it's only down to some pretty impressive detective work from YouTuber and Dreamcast fan pcwzrd13 that we are able to present this demonstration of it. I must point out that the word 'Defense' should really be spelt 'Defence,' but seeing as Titanium are an American studio, I'll give them the benefit of the doubt here.
As stated in the video below, Defense Commander was created as a demonstration of how easy it was to port PC games to the Dreamcast due to the implementation of Windows CE. The game does look fairly basic and has overtones of the Atari Jaguar title Missile Command 3D (albeit without the massive screaming space eels), but it serves as a nice reminder of how the Dreamcast was technically very easy to simultaneously program for. After watching the video, be sure to head over to Titanium Studios' website as they do have some rather interesting (and probably long forgotten) articles relating to Dreamcast development and experimentation.