Mabel Addis collaborated with IBM programmer William McKay to develop 'The Sumerian Game' (also known as 'The Sumer Game') for the IBM 7090 mainframe computer. Addis served as the writer and designer, crafting the narrative, game mechanics, and textual output. The game was a text-based strategy simulation where players managed resources as a ruler of ancient Sumer.

'The Sumerian Game' was initially released and presented in 1964. It was a groundbreaking achievement, making Mabel Addis the first known video game writer. The game showcased the potential of computers for interactive storytelling and complex simulations.

Doug Dyment created an expanded version of 'The Sumerian Game' called 'Hamurabi' in 1966. This version was written in FOCAL for the Digital Equipment Corporation PDP-8. While Addis was not directly involved in this version, it underscored the impact and influence of her original creation.

David Ahl ported 'Hamurabi' to BASIC, further increasing its accessibility and popularity. This version helped to spread the concept of computer simulations and strategy games to a wider audience, cementing the legacy of 'The Sumerian Game' and Mabel Addis's contribution.