Development of CS:CZ was started by Rogue Entertainment, but was taken over by GearBox shortly after. Development was then handed to Ritual Entertainment[1] after Gearbox decided to withdraw in 2002, and Turtle Rock Studios helped out with multiplayer[2]. (Image from https://en.wikipedia.org/wiki/Ritual_Entertainment)
Counter-Strike: Condition Zero is much like its predecessor, CS 1.6, with added graphics updates and a singeplayer campaign, just like multiplayer but with bots[3].
Both images from https://www.oldpcgaming.net/counter-strike-condition-zero/