Texas Instruments Tiva C series launchpad.
I got given one of these just by being friendly to a guy at the makerspace! Fantastic piece of kit. 40 gpio pins on two headers, male AND female pins/sockets. Runs up to 80mhz C++ code, but can run arduino (with a bit of pin and timing-translation). At the moment i’m using one of it’s UART interfaces to control it’s RGB led from my PC at work. Tomorrow, take over the world haha.