Tomu is a super cheap Open Source Hardware 24 MHz ARM computer with 8 KB of RAM and 64 KB of ROM that fits into your USB connector! Of course I had to put Commodore 64 BASIC on it, which can be accessed through the USB-Serial port exposed by the device.
Y. Körber, V. Hahn, M. Moniri, T. Schwartz, and M. Feld. Proceedings of the 13th IEEE International Conference on Intelligent Environments (IE '17), Seoul, South Korea, page 184--187. Los Alamitos, CA, IEEE Computer Society, (2017)