The Northern Reaches will be played using Green Ronin's True20 system, based on the D20 SRD, with some significant changes in places. The major one is that characters do not have hit points, but have wound thresholds that can be gained if a Toughness check is failed against incoming damage. The net effect is that as characters rise through the 20 levels they become increasingly harder to hit due to their skill but remain all too fragile to a well placed blow.
The Fantasy Paths book and the three class handbooks are all available.
Here are some resources for True20: