jonmash designed this simple board with two ATTiny processors powered by a micro USB connector.
Micro USB power input to two ATTiny MCU’s. There are two different ATTinys on this board. An ATTiny84 and an ATTiny85. These MCUs are great because they can be used with no additional components. In fact, on this board, the only additional components are some filter capacitors for the power rail and a header for the programmer interface.
I have exposed an array of copper pads for every pin. This makes it easy to add LEDs or to wire to just about any sensor.
jonmash has shared the board on OSH Park: