My last post I talked about my idea for Rogues. The skills they can do can do by other classes, but they just do them better in exchange for a small hit dice and reduced combat ability.
I probably wouldn't call them skills, but rather tasks. They would be setup so the referee can use them as means of resolving the situations they cover regardless of class.
What about the mechanic itself? I find it useful to look back at the source material and see what they did. While digging through the City-State of the Invincible Overlord I found a rule that Bob Bledsaw used.
Basically if a character felt they could do something extraordinary with an attribute then they got take percentage dice and try to roll under it. Thus a if character wanted to bend bars with his 15 strength he has to roll 15% or lower. They add a few wrinkles about repeated attempts if the characteristic was prime requisite (shades of Castles & Crusades!), and straining yourself if you roll doubles.
I looked at that and while seems like a good starting point I really don't like the percentage roll low. I think D&D works better if you roll high. Plus I want to try to keep percentage dice out of it and just go with a d20. I know that is like newer editions but that one point I think they got right.
However Bob gave pretty low odds of success, 15% for a 15 strength. Plus I want to avoid subtraction if possible.
What I will go with is this. If you want to succeed with a task based on one of your attributes then you need to roll a d20. If you roll higher or equal to a 20 you succeed. You get a bonus for your attribute as follows
16 to 18 +3
11 to 15 +2
6 to 10 +1
3 to 5 +0
Mathematically it works out pretty close. Person with a 15 strength still will only have a 15% chance of success. 18 or higher on a d20.
20 would be an automatic success, a 1 a automatic failure.
In the real world if you are more careful i.e. take longer then you more apt to succeed.
If you are careful it takes 10 times longer to complete the task but you get to add the higher bonus of your intelligence (smarts) or wisdom (perseverance and common sense)
Some tasks (like Spell Research) may have this built in as they always take a long time to do.
Rogues, mentioned in the previous article, will get bonuses to various task over and above the attribute bonus. But they would have sacrificed combat ability or HD because of their focus.
While some will object to any skill system, I think this approach avoids the limitations of the original thief class.