I will begin here with a description of my project cpm4nano - a CP/M-compatible computer based on the Arduino Nano 3.0.

Currently one (!) Arduino Nano (!) in my project:

emulates the i8080 processor, 64 KBytes RAM+additional banks, 4 FDD;
loads the OS CP/M and runs its programs;
exchanges information with PC on the serial port, including uploading files to the emulator using the XMODEM protocol;
with the help of the converter PS/2-UART allows you to enter information from the keyboard;
displays text information on the TV screen (20 rows with 40 cols) (without jitter!).”

Link