I don't think I truly appreciated the potential for the D6 system back when I ran WEG Star Wars in the late 80s. After WEG lost the Star Wars license, they used the core D6 system for other genres.
You can get the self-standing genre books for the Open d6 System for 1.79 each in PDF.
I really need to run an Open D6 Game in the future. The system is simple and natural.
I'll be highlighting free and cheap RPG options over the next week or so...