Although presented as a generic role-playing game, the True20 Adventure Roleplaying book includes four sample settings:
- "Caliphate Nights", a fantastic version of the golden age of Islam, circa 800 AD. A full-color stand-alone hardcover was released for the setting at Origins 2006.
- "Lux Aeternum", a swashbuckling space opera.
- "Mecha vs. Kaiju", in which giant robots protect Japan from giant monsters.
- "Borrowed Time", a setting of Kung Fu action and gunplay against a backdrop of time-controlling conspiracies.
A follow up volume, True20 Worlds of Adventure includes five additional settings:
- "Agents of Oblivion"
- "Blood Throne"
- "Land of the Crane", an Asian fantasy setting.
- "Razor in the Apple", a horror setting in which kids face monsters lurking the neighborhood, inspired by films such as The Goonies.
- 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 ranged from 3-18 (which in other systems would then be cross referenced against a table to convert them 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".
- Instead of experience points, characters automatically increase in level at the Narrator's discretion, usually after one or two adventures.
True20 was originally used in Green Ronin's Blue Rose. Blue Rose won the Gen Con ENWorld Roleplaying Silver Medal for Best Rules in 2005. 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.
- Steve Kenson True20 Adventure Roleplaying (Green Ronin Publishing, 2006) ISBN 1-932442-57-X
- Various Authors True20 Worlds of Adventure (Green Ronin Publishing, 2006) ISBN 1-932442-65-0