Download link:
Download from developer’s website

Chex Quest a licensed id Tech 1 game originally released as a free prize in Chex cereal boxes as a nonviolent kid-friendly alternative to Doom. Chex Quest 2 was released as a free downloadable expansion for the original Chex Quest (although the original website is long gone). Chex Quest 3 compiles both episodes (with some changes and bugfixes), as well as adds a brand new third episode designed by two of the original staff, with new music by the original composer.

Chex Quest 3 comes with an old version of ZDoom. The .WAD archive can be used in any ZDoom compatibile engine (I recommend GZDoom).