Propriety set of roleplaying rules used by GDW for games such as Twilight:2000, Dark Conspiracy, and Traveller: The New Era.
1st edition uses 1d10 primarily. 2nd edition uses 1d20 primarily. Both use d6's for damage and character generation.
System owned by Frank Chadwick. Extant systems using it licensed to continue using it:
Dark Conspiracy - Loren K. Wiseman
Traveller: The New Era - Marc W. Miller.