Awhile back I picked this up, its a Post Apocalyptic RPG by Kevin Crawford, the same guy who did the very awesome Stars Without Number RPG, Other Dust is a separate game in its own right but it is directly compatible with SWN. If you like the work he did for SWN and like P.A. I think you will enjoy this product. It has excellent tables and tags to use to work up your P.A. Sandbox setting, some new classes (they also work just fine with the classes from SWN), mutation rules and other cool stuff. Other Dust is grittier than say traditional Gamma World, with few if any over the top mutations, it comes across as a grim and gritty setting, but with some tweaking you can make it your own. I'll try to post some of the Characters and NPC's I've worked up for my Campaign for ya as examples.
Anyways this is a great product that I frankly don't think gets talked about enough. Even if you aren't looking for a new set of rules for your P.A. RPG of choice the tags and tables alone can be used with your rule system of choice (Mutant Future, Mutant Epoch, Gamma World etc..).
Good Gaming -B.