Last year I bought a Pimoroni Tiny 2040 that I really enjoy playing around with. It’s a fun little device that runs Python. It’s about the size of a thumbnail, has an LED, and you can use the boot select button for user input.
I mainly use it as a cheap USB rubber ducky with a non-malicious script at work (if plugged into a PC, it registers as a keyboard and starts typing: open notepad, write some text about the importance of locking your PC, and then locks the PC).
To do this, install CircuitPython, and follow the instructions of this repository: pico-ducky
Once installed, you can easily write your own rubber ducky scripts and drop them on the device or use existing scripts found here: hak5/usbrubberducky-payloads
I have a small git repository that I use as a template to start off with, it includes all the required libraries and a slimmed down and modified rubber ducky parser: ryanschulze/rubber-pico-duck
The LED on the pico 2040 will glow dim blue when it has completed initialization and is ready, if you press the boot select button, the LED will turn red and it will execute the payload, when complete it will flash green briefly before returning to the ready state (dim blue).