Beats of Rage is a freeware open source video game and moddable game engine made by Senile Team and inspired by Sega's classic Streets of Rage series. The term "moddable" means that the program allows users to create their own content, and thus their own beat-'em-up game, which is then called a "mod".
The engine is customisable, and allows for new games to be built on it. These are distributed in a custom PAK format. The games developed for the Beats of Rage engine are commonly referred to as "mods", the creators are commonly referred to as "modders", and the engine itself is commonly referred to as "moddable".