I've just brought and is playing Knights of the Chalice (thanks for the reference, guys!). I have a few gripes with how some of it is implemented, especially since I've had some surprises with how Darkness functions (you're not blind, you can still target creatures with no problem, even shooting from INSIDE a darkness effect at somebody far OUTSIDE it!). Overall fun though, it has the feel and handling of roughly what I was missing in my DnD games.
Right now I'm in thinking mode with regards to the whole OGL thing. As far as I understand the wording, there must be no "hidden data" in the sense of rules for monsters, spells, etc. The way I see that Knights of the Chalice has done this is by making every effect, spell and so on a link to a help page that explains everything down to the very conditions. In essence, if you sat down and read through all the rules and so on, you could be playing Knights of the Chalice PnP. I think this is in the spirit of the OGL and hopefully also RAW (LAW? Law As Written?)
At this point I will probably be holding my cards closed and simply develop the engine as a learning exercise, both of my programming skills, design skills and of my grasp of the rules. If/when it becomes viable to release I'll take more serious steps to evaluate the situation.
You've all been very, very helpful with this. Thank you all very much.