[krajzeg]

The GBA still had some cartridges with enhancement hardware, though a lot less focused on overcoming CPU/memory limitations than on the previous consoles.

My favorite is WarioWare: Twisted [1] including a gyro sensor (+ a rumble pack) to enable gameplay based on turning the whole GBA around. But there were also add-on real time clocks (Pokemon), light sensors, and other things.

It also had the Nintendo e-Reader [2], which technically connected to the cartridge port and loaded like a cartridge, but was its own unique piece of weirdness.

[1]: https://en.wikipedia.org/wiki/WarioWare:_Twisted!

[2]: https://en.wikipedia.org/wiki/Nintendo_e-Reader

[mmaniac]

I like the Play-Yan adapter. It's an official media player which includes its own DAC and headphone jack, avoiding the GBA's own disappointing audio DAC. It also adds hardware decoding[1] - the GBA's CPU is a little too puny to handle media playback by itself.

[1] https://shonumi.github.io/articles/art32.html

[bombcar]

https://www.theverge.com/circuitbreaker/2017/9/21/16339122/e...

GBA medical device.

[Keyframe]

GameBoy vehicle diagnostics tool https://www.motor1.com/news/701772/game-boy-diagnostic-cartr...

[bena]

I had forgotten about the eReader. I had gotten Excitebike on the eReader card because I was curious. I was planning on getting an eReader at some point, but never got around to it.