Jorj Bauer has created a handheld Apple IIe emulator with a Teensy:

Aiie! – an embedded Apple //e emulator

Teensy 4.1 (600 MHz arm Cortex M7) running a full-speed Apple //e emulator. Because everyone needs one of these, right?

The OSH Park boards arrived, and I spent some time Monday assembling! Here’s a time lapse of the build, which took me shy of 3 hours (mostly because I hadn’t organized any of the parts and had to hunt for several).