Chex Quest was a DooM total conversion (TC) developed by Digital Café, and released as freeware by Ralston Purina on boxes of Chex Cereal as a promotion back in 1996.  Chex Quest consisted of a five level episode in which the player got to take on the role of the Chex Warrior and rid the peaceful planet of Bazoik (Yes.  Bazoik.) of the evil mucus based life forms, the flemoids, which have invaded from another dimension.  Upon completion of the game, users were told to go to chexquest.com, where they were able to download a second episode, Chex Quest 2, in the form of a patch wad. (Note: chexquest.com still exists, but no longer has anything to do with Chex Quest.)

The Chex^®Quest CD-ROM and its decorative cover sleeve.

Chex Quest was touted as a “non-violent” game, despite the fact it was a (very slightly) modified version of DooM.  Supposedly, none of the flemoids were ever actually killed, but were simply teleported back to their home dimension via the “zorch” energy fired from the player's weapons.

The original Chex Quest Intro movie

In 2008 Charles Jacobi, the original art director for Chex Quest, released Chex Quest 3, the third official installment of the game. Chex Quest 3 is available for free from Chuck's website, Chuckopolis.