I'm planning a project to create a retro-clone of a non-D&D game. The problem is that I specifically want to restate the mechanics of the game as faithfully as possible, but I'm not sure how to handle things like the skill list and skill names, spell names, a mechanically-central set of tables, and other things that are in the "grey" area of functional versus presentational and hence uncopyrightable versus protected expression.
To sort this out, I want to see what has worked in the past and what compromises other retro-clone authors have found necessary. I know there are lots of D&D retro-clones using the OGL, and lots of non-D&D games using the OGL that are not retro-clones. Unfortunately, most retro-clones solve the problem by either deriving presentational elements from another OGL'd set of rules (e.g. skill names from d20 SRD), using a different set of rules (e.g. Mutant Future is mechanically unlike Gamma World), or by getting a license/permission from the original game's author (e.g. ZeFRS has Zeb Cook's blessing). I don't have an OGL game to derive from, no license, and I don't want to change the mechanics unless absolutely necessary.
So, I'm looking for examples of other OGL games that:
- Clone a game's mechanics without deriving from an OGL set of rules
- Created by someone without rights to the original game
- Licensed under the OGL (so I can see how they pulled it off)
All the games listed in the Wikipedia article on Open Gaming are disqualified either by (1) or by both (1) & (2). In fact, the coverage of "retro-clones" in that very article makes "retro-clone" out to be synonymous with "D&D simulacrum".
It might be that the answer is "none exist", but even that would be useful information for me to move forward with.