There's a lovely device called a PiStorm, an adapter board that glues a Raspberry Pi GPIO [General-Purpose Input/Output] bus to a Motorola 68000 bus. The intended use case is that you plug it into a 68000 device and then run an emulator that reads instructions from hardware (ROM or RAM) and emulates them.
Unlike many handheld devices that force you to choose between typing and tapping, KeyMO gives you both. It feels like a mini-laptop that can still slip into your bag.