Another excellent book from Kevin Crawford.
I've been looking for a good post apocalyptic system for a while and this one pretty much ticks all the boxes for me. It is a lot less gonzo that Gamma World or Mutant Future, but because the core system is pretty much OD&D, you can very easily bring stuff across from systems like that. The negative mutations can perhaps be a little excessive (it is possible to create a character with no head), but that sort of thing is so easily house ruled away it really isn't an issue.
As with Stars Without Number, the GM's section on sandbox world creation are fabulous - and as with SwoN system agnostic.
[5 of 5 Stars!]