From publisher blurb:
Apocalypse Essentials is a standalone product which uses a slightly simplified version of the Transdimensional Adventures rules system. The rulebook includes everything needed to play including combat rules, skills, character generation including mutant, mutant animal and robot PCs, vehicles, and monsters. It may also be used as a supplement to add post-apocalyptic rules and content to a transdimensional campaign, including:
Post-apocalyptic and relic equipment lists and costs.
New mutant types (Preserved One, Small Folk, Denier, and Multimutant) and minor mutations e.g. Mutant Talents.
Post-apocalyptic creatures and encounter tables.
A sample campaign region & map.
Other content including diseases, revised professions, and new talents.