The Z-Berry is a retro single-board computer that shares a form factor with the Raspberry Pi, but is built around the  Zilog Z80 processor. The Z-Berry runs at 10MHz, the board has 512 KB of RAM, along with 32 KB of ROM used to store the firmware, although it does have 17 chips on the board, rather than four. The board uses a micro SD Card for storage and, as well as a serial interface both I2C and SPI buses are present, along with a Raspberry Pi lookalike 40-pin connector exposing almost the entire Z80 bus. The board also has a piezo buzzer, a PS/2 style keyboard connector, and is powered via a micro-USB connector. It all fits inside a standard Raspberry Pi case. Sadly the Z-Berry is not available for sale directly, but Martin has provided a full bill of materials and instructions allowing you to build one yourself.