dm4hire
Explorer
In my mind, the Cortex rules (Serenity, Battlestar Galactica) is an outgrowth of this system - you simply remove the d20 from the d20 + dX roll. The two systems are close enough I used the Cortex rules with the Alternity Gamma World rules with minimal fuss.
Cortex is very similar I agree, but I think the most unique aspect of Alternity is that you're trying to roll low with varying degrees of success having an impact. It's the RPG world's version of golf, only no walking and a lot more entertaining.
I wouldn't mind seeing a variant of the system either if people didn't have a problem converting D&D over to it.