I just got a TRS-80 last week and I've been programming for it. This program displays 3D wireframes using polygons! The camera can also move and zoom, which helps show that there is actually depth.

Here are some pictures:

Here is a cube rendered by the program.

(http://i.imgur.com/FCKLkcs.jpg)

Here is the same cube, with the camera manipuated so that the cube can be seen better.

(http://i.imgur.com/yX8V3uR.jpg)

Here are the coordinates of the cube. Each data statement holds coords for one polygon, and they are structured like this: DATA x1,y1,z1,x2,y2,z2,x3,y3,z3

(http://i.imgur.com/D7OP4VT.jpg)

I'll be posting source code soon.