BSG and Serenity were the Cortex system.
Firefly and IIRC Smallville is the Cortex+ system.
The new thing is Cortex Prime.
So basically it is Cortex 3rd edition.
Sort of. Because it's got a core system in it, but quite a lot of GM toolkit bits. You could pick the options which most closely mimic Cortex+, or you could bolt together something rather different.
It's all about selecting whether your game style/setting needs the bits which are all about relationship maps, beliefs to challenge and abstracted skills (like "soldier"), or the more granular skill list and action movie bits.
It's pretty nice in the Cortex+ iteration. I haven't played it much - a little Firefly, and a really good one-shot based on Leverage.
I got all excited for Cortex Prime, and went so far as plotting out a "space station SF" setting along the lines of Babylon 5 or Deep Space 9 with one of the earlier system documents from the Kickstarter. I've still got the (unplayed) notes. I might go back to it when the book arrives, which I'm again quite excited by.
I really liked playing and running it with Firefly.
Liked playing it with Marvel Superheroes.
Would be very interested in Hammerheads the International Rescue style game they have up on the C Prime website.
I was quite excited about using Cortex Prime in dramatic mode as a crunchier replacement for Fate in my operatic tragedy steampunk games. But that was 3 years ago when the Kickstarter was running, and my interest has waned. I'm waiting for the final book to drop through my door to see if it can reinvigorate my excitement.
I was going to try having either Values and Relationships or Roles and Relationships as my primary sets of traits, to make it very character focused rather than story focused.