I was thinking about using a simple RPG system for a potential game of Nightspawn/Nightbane. Generally you could use it for everything anyways.
So the game would be based on 1st edition The Dark Eye/DSA (a simple d20 roll under system with 5 stats), but there would be one big difference:
Instead of an active parry or modifiers to make ability rolls harder, difficulty would be expressed, by a a value that you are not allowed to roll under.
So if an opponent has a Parry of 4 in this system, you only hit him if you roll above 4, but below your attack value (e.g. 10).
But to make things more interesting, the higher you roll (but not above your value!), the better the result is. Therefore someone with a really high ability can get special successes. (This aspect could be similar to the the Dragon Age system, but I did not read this one yet.)
If you know Unkown Armies, you will notice certain similarities.
The system would also include Tricks (based on any stat/ability), like Savage World does. This could also be influenced by page 42 of the D&D4 DM Guide.
(Something else I like a lot are aspects from FATE, but I am not sure, if they fit this system or make it too complex.)