Or something like http://www.heavygames.com/snake3d/playgame.asp?
With or without transparency (I'm confident in the nspire's performance )?

You mean controls similiar to a rubik's cube?
(Except rotating the individual rings of course)

Edit: FPS counter works now. 100+fps in wireframe mode,  50 in color mode, 30 with textures and 25 with interpolated colors.
But I get some issues with the keypad/touchpad interrupts. If I enable IRQ 16, it just freezes on the real calculator, it works on the emulator.
I acknowledge by writing ~0 to 900e0008 and 900e0044. Can someone give me a clue what might be wrong here?

UPDATE! 

I made some progress on nGL and made another demo (which is again, not intended to be "played"): crafti!

Changes:

• Faster! A lot faster, actually. I can't tell any numbers, but with large triangles it went from slow to smooth
• Interpolating colors between vertices, which is actually slower than textured rendering
• Prefixed functions with ngl (for example nglInit)
• Something like vertex arrays (nglAddVertices)
• Wireframed rendering
• Doesn't crash anymore
• Some documentation
• Clipping! (X: Per pixel Y: Per line Z: Per triangle)

Todo:

• Colored textures (non-interpolated)
• Compressed textures (zlib). nGL doesn't lose performance with higher-resolution images, they just get too big in raw format
• Make a real, playable, good looking game which uses nGL
• FPS counter

It looks a lot better on the emulator and on calc than these gifs (byzanz-record is crap):

(The emulator runs at 90% speed here, I accidentially hit F9)

The textures used aren't mine this time, terrain.png came from http://www.planetminecraft.com/texture_pack/fancycraft-by-jjjas0n-64x64-version-100.
Also, the controls (same as nGL in the first post) are a bit weird to use on a PC so the twitches you see are just my fingers finding the keys.

It's a bit slower on calc than on the emulator, I suspect it's the touchpad polling every frame, but if that get's a real issue, I'll take care of that.
If you want to use nGL, grab gl.cpp, gl.h, fastmath.h, fastmath.cpp, fix.h and don't forget to read gl.h and #define SAFE_MODE in gl.h!

Anyway, the pin for the audio player is not adjacent and completely different.

Wrong, RX,TX,GND,GPIO

I removed the battery BEFORE soldering, so nothing bad can happen even if you short the pins. Just look at the pins several times at a different angle so you can be sure not to short anything, and then insert the battery again. My calc still lives after several solder sessions.

Now almost everything is twice as large, bold and a really ugly font..
I disabled caching completely and did a full reload.

I actually like the appearance. I don't have FiraSans on my laptop, but it seems to fallback to droidsans, which I like even more!
But the kerning looks awful..

Beware: It's written in C++ (with Qt), source code and binary for x86_64 linux attached. It's sort of hacked together (doesn't even show whether the file exists), but it should work.
./ConvertImg test.png >> textures.h and then #include "textures.h" and use the texture with glBindTexture(&test);

Not really, it needs three division per horizontal line (z, u and v) and the pixel() function checks whether the pixel is visible (clipping and z-buffer). It basically scales linear to height, but I'll improve that once I implement triangle clipping.

Edit: If you're reading this and getting confused, this is a reply to the second last post