A: No. The Atlas can be used with any fantasy TTRPG, though Cairn (which is free) is recommended.
The book describes over three dozen distinct lands and nations, such as the undead nations and states ruled by evil sorcerers, each designed to be easily "looted" and dropped into a homebrew campaign. Key Features and Mechanics
The "Latter Earth" is not a typical fantasy realm. It is our planet, billions of years in the future. High-tech Legions have collapsed into sorcerous fiefdoms. The sun is dying. Reality has been patched and re-patched by previous "Iterums" (prior versions of existence). Magic works because the laws of physics are essentially a bloated, buggy operating system.
Beyond geography, the atlas might offer insights into how societies have restructured in response to these changes. It could highlight new global powers, areas of conflict, or innovative solutions to the challenges faced by humanity.