Out Zone was released in August 1990.
Several characters from other Toaplan games make cameo appearances as powerups or bonuses :
Six plane squadron from "Flying Shark
" fly on the screen shooting enemies in an upside down V shape pattern.
The "Truxton" ship follows the player helping out.
ZIG-01 from "Zero Wing
" flies on the screen dragging a bunch of '5000' points bonuses.
Pipiru, Toaplan's mascot from "Zero Wing
" can be summoned in level 1 from shooting a hole in a rock. It is vulnerable to all weapons, but it will bring a significant score bonus if safely taken to the level's boss.
Pony Canyon / Scitron released a limited-edition soundtrack album for this game (Out Zone, Snow Bros. - PCCB-00044) on 21/10/1990.