Microsoft’s Z-80 SoftCard allowed Apple II users to run CP/M software by utilizing a secondary Zilog Z80 processor, facilitating memory sharing and enabling coexistence with the existing 6502 processor. The SoftCard remapped memory to avoid conflicts and included a detailed manual for programming, including challenges of managing interrupts and memory addresses.
https://devblogs.microsoft.com/oldnewthing/20251104-00/?p=111758