Over at The2Bears, they've spotted a cool piece of DS homebrew, called Maelstrom DS, and clearly an abstract 3D tribute to classic arcade title Tempest.

Excerpting from the tech information: "Much of the code for MaelstromDS is the same as that in the original GBA version, the major change being that the DS has 3D hardware built in, and therefore there is no need for the code to transform the scene into 2D lines. Additionally, the view can be moved by touching and dragging the screen."

What's more: "Finally, the transparency of the outside of the tunnel is achieved by drawing the tunnel twice. Once with the polygons set to solid and the front faces drawn, then with the polygons set to half transparent and the back faces drawn. This is necessary because the DS cannot correctly handle multiple transparent polygons drawn on top of each other." Cute tech information, fun title!