Firefly RPG
I ran the Serenity RPG for a while years ago, and we all enjoyed it very much. I was saddened when it they did not renew the license and make more content. Fast-forward a few years, and they produced the Firefly role-playing game. I recently finished running a group through it, and here are my thoughts overall about the differences...
Very short version: Firefly RPG takes the trend of abstracted RPG too far for my tastes. The group is generally in agreement we will be going back to Serenity RPG.
Longer version:
If you would like to see the longer version, please post comments requesting this, and I will write it up.