Beats of Rage is a fan-made tribute game to Sega's Streets of Rage series. It supplants the original graphics and characters with resources taken from The King of Fighters series, albeit with tongue in cheek renames. Originally developed by Senile Team, the underlying engine powering Beats of Rage later went on to become the Open Beats of Rage (OpenBOR) game engine project.

        UP # MOVEUP                A # ATTACK1
        DOWN # MOVEDOWN            X # ATTACK2
        LEFT # MOVELEFT            Y # ATTACK3
        RIGHT # MOVERIGHT          B # JUMP
        SELECT # SPECIAL          R1 # ATTACK4

                     START # START

OpenBOR games are usually non-commercial games made by fans.

However, some of them are ripping sprites and sounds from other games, which actually are under copyrights.

As for any other type of ROM, Google and search engines are the best way to find PAKs for OpenBOR.