The Z-Berry is a retro single board computer that conforms to the Raspberry Pi form factor and built around the Zilog Z80 processor. The Z-Berry runs at 10 MHz [20 MHz is possible], is orders of magnitude slower than the quad-core 1.2 GHz ARM-based Broadcom processor in the Raspberry Pi. The board has 512 KB of RAM, along with 32 KB of Read Only Memory (ROM) to store the board’s firmware.
Z-Berry uses a micro SD Card for storage and micro-USB for power, a PS/2 style keyboard connector, piezo buzzer, as well an I2C and an SPI bus. Being the same size as the Pi, the Z-Berry fits inside most of the Raspberry Pi cases and also includes a 40-pin connector exposing almost the entire Z80 bus.
While the uses for the board are obviously more limited than the Pi, the Z-Berry has been demoed playing a numbers-themed Tetris clone called Numeris, on its attached 0.9-inch, monochrome I2C OLED display. Sadly the Z-Berry is not available for sale directly, but [Martin K] has posted a lot of details on how to make your own Z-berry which includes the BOM, schematic and preliminary information to build one yourself. The entire board can be put together for around $28!