So you are looking for a tiny computer that fits inside a USB port? Tomu is just the board for the job. It has two LEDs to let you know what’s happening and two buttons. Tomu has an open design, so you can make your own circuit board and load your own programs.
This tiny board has 8kb RAM and 64kb flash storage. It is based on a Happy Gecko EFM32HG309 microcontroller. Looks pretty promising if you ask us. More info is available here.