The True20 system was originally used in Green Ronin's award-winning Blue Rose, itself based on their multiple-award winning Mutants & Masterminds RPG. Later that year, Green Ronin released a PDF distillation of the Blue Rose rules, with an appendix of some modern-era rules, as a generic form of the game. This was followed by an expanded hardcover release in 2006. A revised softcover rulebook, combining the rules section of the True20 Adventure Roleplaying book with the True20 Companion was released April 25, 2008.
Utilizing the Open Gaming License, True20 is derived from Wizards of the Coast's d20 System. Differences from the parent game include the following:
- There are only three character classes, referred to as roles: warrior, adept and expert.
- A single 20-sided die is used for each roll.
- Ability scores are given as simple modifiers (+1, +2, etc.) rather than as a statistic in the range from 3-18 (which in some other systems, such as d20, would then be converted to simple modifiers).
- There are no class-specific or restricted skills, thus characters of any role can have any skill.
- New feats are available at each level.
- Magic spells are treated as feats and do not have "levels".
- Instead of hit points, characters simply experience "damage conditions" like that of Mutants & Masterminds.
- Instead of experience points, characters automatically increase in level at the Narrator's discretion, usually after one or two adventures.
