Labyrinth Lord...or some other system. We'll have to give Urutsk a look-see again as well. Maybe it could be adapted to another setting? That might be interesting...in any case, wish the new marshall luck. She'll need it.
EDIT1: We've decided to develop our own system outside the OGL (for now) in order to better address some of the more unique features/aspects of the Riskail setting. As we develop the setting further, it is our intention to make it a place that could accomodate nearly any system you choose to use to explore it. We do not feel a burning need to flog off one more RPG system on folks. Our focus is on Riskail, first, last and always. If we do revise some OGL system like say Labyrinth Lord, we'll provide details on that sort of thing over at Old School Heretic.
EDIT2: We'll be posting a series of articles that deal with the development of our in-house System over at Old School Heretic. The Gaming Session reports will get posted to the Netherwerks Blog. What we're going to post here at the Riskail blog will be the maps, background details and setting info concerning the Reservoir Keep, Misericorde Canal, and other Locales, Setting Details, or Persoanlities the new River Marshall runs into, encounters or crosses paths with in the course of her adventures. There's also a few pieces of fiction based upon several of her predecessors and at least one contemporary that will likewise get posted here as well. It should be fun. Hopefully she'll steer clear of the Ragers, Veiled Riders and other such things until she's ready to take them on.