Earth
From RPGWW Wiki
A planet a lot of offworlders come from, including Cardinal, Shakti, El-Bob, Kate's blue girl (Sara?), and... others. I'm SURE.
In retrospect, it can be seen that there must be multiple Earths. The Earth of one offworlder is often different from the Earth of another. We try not to get into this too deeply.
Also, DF (dark future) took place on Earth. In the future. A dark future.