Ten million* different ways to do skill checks in RPG.

There are many ways to do skill checks in roleplaying games. So I made this system of tables so that you can generate your own system. Basically start with the Narration table and randomly choose one of the results listed, then replace all bold words with content from the corresponding table. Repeating until you get a description of the method. Some of the tables says something like Randomize( stat ), this means to replace stat in the resulting expression with what ever it was you where randomizing (or computing or rolling etc).

* It is actually a bit more than ten million.

Tables

Narration:

1. The player describes how to do it, and the gm decide if it will work.
2. The player makes a check, then narrate their success/failure
3. The player makes a check, then the gm narrate their success/failure
4. The player makes a check. On success the player then narrate how they do it. On failure the gm narrate what happens.
5. The player makes a check. On success the player describes how to do it, and then the gm decides if it works.
6. The player describes how to do it, and if the gm decide that it could will, the player makes a check.
7. The player describes how to do it, and the gm decide if it will work. If the gm decides that it doesn't work, the player makes a check anyhow.
8. The player describes how to do it, and the gm modifies difficulty based on description, then the player makes a check.

Check:

1. Compute skill then succeed if better than compute difficulty.
2. Compute difficulty, then succeed if better than compute skill, on failure, retry.
3. Randomize constant, then succeed if not better than skill worsened by difficulty.
4. Randomize constant, then succeed if not better than skill worsened by difficulty, on failure, retry.

Better*:

1. higher
2. lower
3. higher or equal
4. lower or equal

Retry:

1. you may spend meta currency to reroll all dice.
2. you may spend meta currency to reroll any number of dice.
3. you may spend meta currency to make a new check.
4. you may spend meta currency equal to difference to succeed anyway.

Compute( stat ):

1. Take stat.
2. Spend meta currency to improve stat.
3. Randomize stat.
4. Spend meta currency to improve stat, then randomize the result.
5. Randomize stat, then spend meta currency to improve the result 
6. Randomize stat, then spend meta currency to improve the result, then randomize the result of that.

Randomize( stat ): 

1. Roll dice pool equal to stat, and pick one.
2. Roll dice pool equal to stat, and add them up.
3. Roll dice pool equal to stat, and get one success for each value better than constant.
4. Roll dice pool equal to stat, and get one success for each value better than better than upper constant, but subtract one for each value worse than lower constant.
5. Roll one die with the number of sides equal to stat.
6. Roll die and improve the result with stat.

Dice Pool:

1. Dice size.
2. Dice size, exploding

Dice Size:

1. d2
2. d6
3. d8
4. d10
5. d20
6. d100

Die:

1. 1d20
2. 2d10
3. 3d6
4. 3d6, exploding
5. 4d100 - 2
6. 3d20, choosing the middle die
7. Three fudge dice
8. 2d10, subtracting the lower from the higher

Exploding:

1. When a die is rolled with max value, you roll an extra die and add its value.
2. When a die is rolled with max value, you roll an extra exploding die and add its value.
3. When a die is rolled with max value, you remove it and rolls two extra dice and add their values.
4. When a die is rolled with max value, you remove it and rolls two extra exploding dice and add their values.
5. When a die is rolled with max value, reroll it using a one step larger die.
6. When a die is rolled with max value, reroll it using a one step larger exploding die.
7. When a die is rolled with max value, you roll an extra die one step larger and add its value.
8. When a die is rolled with max value, you roll an extra exploding die one step larger and add its value.

Constant:

1. Just make up a number that seems to fit the context.

* If lower or lower or equal is better, then improve means decrease, otherwise it means increase. worsen means the opposite of improve. only roll for better once and use the same result for every instance.

Examples

The player describes how to do it, and the gm modifies difficulty based on description, then the player makes a check. Roll one die with the number of sides equal to 10, then succeed if not higher than skill decreased by difficulty, on failure, you may spend meta currency to reroll all dice.

Roll d6 equal to 3, and get one success for each value higher than 4, but subtract one for each value lower than 2, then succeed if not higher than skill decreased by difficulty, on failure, you may spend meta currency equal to difference to succeed anyway. On success the player describes how to do it, and then the gm decides if it works.

The player describes how to do it, and the gm decide if it will work. If the gm decides that it doesn't work, the player makes a check anyhow. Roll d100 equal to difficulty, When a die is rolled with max value, reroll it using a one step larger exploding die, and get one success for each value better than 13, then spend meta currency to decrease the result, then succeed if lower than or equal to roll d100 equal to skill, and pick one, then spend meta currency to  decrease the result, then roll d8 equal to the result of that, and pick one, on failure, you may spend meta currency to reroll any number of dice.

Conclusion

The system as it stands is a bit limited. It can't handle more than two degrees of success. No fumbles or critical hits or partial successes. If expanded with features like that you could likely generate billions of skill check systems!

But no, I don't really recommend you to use this system to generate rule systems. The point is rather to show how much variation there can be in how to do something as simple as skill checks. In particular I want focus on the first table Narration. It is in many ways the least mechanical part of the skill check, and something many rule books skip over, but I think really important. The different alternatives to a large part corresponds to different play styles. Number one of course being freeform. Number two would be Story Now game. Four corresponds to Apocalypse World. Seven has aspects of old school in it. (Saving throws can be seen as being allowed a skill check after having chosen badly.) Six and eight seems to be really common, but makes very little sense to me. For eight, I think that if the gm can make a good estimate of the difficulty, they can just as well estimate the outcome, and no roll should be necessary, while for six, it just results in explainable failures, and random gate-keeping.

The more I think of it I actually really prefer number seven. It allows you to play a character better than yourself, and to use player skill, while avoiding the problems of six.