Ever since my interest in D&D began to wane in the late 80s, I've toyed with developing my own homegrown, generic RPG system. My ideas have gone through numerous iterations, inspired by countless published games, and those ideas have begun to coalesce around a system I call "Kevin's Krawl" (which I discussed last year). The task resolution system uses two 6-sided dice, to which attribute and skill modifiers are applied. It's quick, easy, and takes advantage of all the D6s I have floating around. I'm pleased with it, and have been pleased with myself for creating it.
Recently I was reading a copy of the Traveller RPG rules (the little black books from the 70s).
I realized that I did not create the 2D6 system. Traveller was using it 40 years ago, and I just ripped them off! Goes to show that sometimes tried and true methods work.