The R. Talsorian sourcebook for Cyberpunk based on Walter Jon Williams' book Hardwired (1986) included some interesting variations on the core rules. Most significantly, the netrunning rules were revamped to a more realistic system. CP2020 is a good game, but the treatment of cyberspace is very idiosyncratic, to say the least. Another thing I like is the table of "glitches" for NPCs. These are personality quirks that can give characters a distinctive personality. It's like a quick-and-dirty Life Path. To determine the number of glitches, roll 1D10. 1-5 = 1 glitch, 6-8 = 2 glitches, 9-10 = 3 glitches. Roll 2D10 for each glitch and cross-index on the Glitch Table.