To expand a bit on my comments here on how it's difficult to write new rules for GURPS: It's not hard to add entirely novel rules to GURPS. The problem, in my own writing and gaming, is finding a need to add entirely novel rules. Mechanically, it's not necessarily hard to write new rules. GURPS is heavy on "find the appropriate trait, modify for circumstances, and roll that number or lower on 3d6." And there's always room for special cases. For example, Tactical Shooting and Technical Grappling add a wealth of gritty detail to shooting things and grabbing people, if you're into that kind of thing, and even with the basic magic system, basic psi, a magic-as-advantages approach, RPM, and variants to be found in Thaumatology , there's always room for new approaches to extra-normal abilities. No, what I'm talking about is finding topics on which new, general rules can be written where none existed before, or broadly applicable rules for notab