"My question concerns the skill system that you pointed out (Skills: The Middle Road).  Could you give me a little more background about how you use the system?  Is the system only used for opposed checks, or can the system be used for "static" checks (like using blacksmithing to make a horseshoe or to recognize a statue using a knowledge of ancient history)?  Do you use "static" checks like that in your game?  If not, how do you determine what the player knows?

Do you compile a list of defined skills that the character has when he is created or is it "free form" and it is determined if the character has the skill (and what to what level he has mastered it) when the player makes a decision that would require a check?"

Sure! I'd be glad to talk about Skills: The Middle Road. It's a great system, and I love it! It's a good system because it's simple, skills aren't tied to level, and it doesn't prevent any player from attempting skills.

Many of your questions are about how people use skills in general. I talk a lot about skills and how to use them while maintaining agency. Let's take a look at your questions.

I would say that I use the system almost universally just for static checks. But often they are static checks for character abilities, not player knowledge. This is because I am unconcerned about mechanically representing what the player knows - I talk about it at length here, but in the example you gave, what would be gained by preventing them from making a horseshoe or recognize a statue? Neither of them improves the game. 

Do you compile a list of defined skills that the character has when he is created or is it "free form" and it is determined if the character has the skill (and what to what level he has mastered it) when the player makes a decision that would require a check?"

That depends on the campaign. For a traditional D&D campaign or sandbox driven by player involvement, I usually keep a fairly free-form system, allowing players to pick whatever skills they feel they need to define their character. For Numenhalla, my megadungeon campaign, I have a very specific list of skills, each with a very specific mechanical function.