The d20 Master Table is a handy visual reference for any rpg that uses a single d20 compared against a target number, including the basic d20 system, Green Ronin's True 20, and the upcoming Passages game from Blue Devil Games (and the Bullseye20 system it's based on).
In seconds, the d20 Master Table gives you the chance of success for any check given the bonus/penalty and the target number/difficulty class. The table can be used when creating adventures to properly scale encounters and at the table to tweak DCs "on the fly" based on the specific circumstances. For example, maybe you created a DC to open a lock assuming the party's resident lockpicker would be present. Unfortunately, the rogue was captured in the last fight. Using the Master Table, you can scale the challenge to the same level of difficulty based upon who is attempting to pick the lock now. Or perhaps the party has gone off the beaten path and is attempting something you hadn't planned for. Now you can create a DC based on what you perceive is the appropriate chance of success.
True 20 is a trademark of Green Ronin Publishing, used with permission.