PETCHESS 4000 from Philidor Software came out in 1981. The author is unknown, however a similar looking program called MICROCHESS 3 was released in 1984, therefore it is possible that the chess engine was written by Peter Jennings who wrote the original MICROCHESS in 1977 for the KIM-1. It is unclear whether the program was modified for the MICROCHESS 3 version. The chess board and screen have a different color in PETCHESS 4000.
To access the game options, you press: ] then followed by the letter. ie ] + L = Levels, ] + N = New Game. ] + H = Help (The Help screen will show you all the options and setup commands available in the game).
The game is enjoyable to play and has a fairly decent openings library.
You can see MICROCHESS 3 for the Commodore 64 here:
Estimated rating for PETCHESS 4000 is 1100 - 1200 ELO (1300 - 1400 USCF).