HAT, or HP - AC - TWENTY SIDED, is a roleplaying game that shares three basic concepts with D&D but diverges from there. The three concepts kept from D&D are obvious from the title: HP, AC, and the D20 roll. However, each is expanded in scope.
Here we define Aspect traits in much detail, which are the most powerful in the game but also come with some stipulations making them a bit tricky for the GM and hopefully more fun for all at the table because of this dynamic.
This page also explains the basics on how to manage creating new Aspect traits inside the HAT system. In order to do so, you need to already understand the basic terms. These rules all require active participation of the GM, as directed in the following text.
Aspects can be broken down into the following types: Histories, Natures, Beliefs, Legends, and Uniques. Overall though, each Aspect trait is a sweeping characteristic of your adventurer that says a lot about them. Each also tends to override one or more assumptions about the character (see Traits).