A bit confused, but will figure it out later, because there are several books for it:
Based on naming conventions, some of the write-ups, and the bundles in RPGNow (see below), there are at least two different rulesets (Match System or Storygame) for the setting:
Also, according to the Setting Guide, you're free to approach the setting (if you didn't already know that you're allowed to used whatever ruleset you want) with you whatever ruleset you want:
"You should be able to play in the equinox setting with any generic game system available. Cortex, D20 Future, Fate, HERO, GURPS, Savage Worlds, Open D6, TriStat, Unisystem, etc—all of these feature all the mechanics needed for this and come with guidelines for adapting futuristic settings. Just add a shot of magic!
In case you seek to make your adaption 'official:' we’re open for submissions. Contact us and we’ll find a way to get your rules adaption out in the open."
Sounds like a plan. Time to add these to the read pile! Setting first, of course.