David Johnson-Davies created a printed circuit board for his ATtiny85-based Secret Maze project.
Check it out here!
To avoid the need for an on/off switch I’ve updated the program to automatically go to sleep if there has been no keypress for 30 seconds; this has the advantage that it’s not possible to inadvertently leave the game on, and run down the battery. To wake up the game you press the button labelled On on the PCB. The power consumption in sleep mode is about 0.25µA at 3V, which is negligible.