This is a small adapter, in the form of a daughter board, which fits into the socket of the "Sally" CPU of the Atari 800XL microcomputer. It replaces that CPU with a CMOS, modern, low-power, fully static, currently in production W65C02S and some auxiliary logic. The project has been featured in three videos in my YouTube channel ("The Byte Attic," https://www.youtube.com/channel/UCfzZNuoHys1t-AdwYDhOz8g).
Why do you think that https://github.com/temisu/ancient is a good alternative to Sally-to-W65C02S-adapter