Zero Gunner is a shoot 'em up developed by Psikyo and released in 1997. The arcade game allows for eight-way movement using a joystick and supports up to two players at a time. It was notable for its lock on targeting mechanic that allowed players to rotate around targets. The game was succeeded by a sequel, Zero Gunner 2 for the Sega NAOMI/Dreamcast. Source: Wikipedia, "Zero Gunner", available under the CC-BY-SA License.