Doom
Doom is a shareware game of three episodes, each having eight standard levels and one secret level. The secret level in each episode is accessed by finding a secret exit in one of the normal levels. The episodes are Knee-Deep In The Dead, The Shores Of Hell and Inferno. In the shareware version the only episode that can be played is Knee-Deep In The Dead. The expansion pack of Doom is Ultimate Doom, which has the fourth episode, Thy Flesh Consumed.