Commander Keen in Keen Dreams is the second game of the series, released in 1991 as a single episode; it is sometimes referred to as episode 3.5 of the series. It was developed for MS-DOS by id Software, which had been founded by the Ideas from the Deep team after the success of the first game, and published through Softdisk as part of an agreement between the companies as the founders of id had been employees of Softdisk when they developed Vorticons. Id used the game, which stands outside of the general continuity of the series as a "dream" episode, as a prototype to test ideas they wanted to use in future games, such as a more advanced art style, parallax scrolling, and gameplay changes. In 2013 a port was developed by Super Fighter Team for Android devices, and a 2014 Indiegogo crowdfunding campaign led to the original source code being released under GNU GPL-2.0-or-later and a release by Hard Disk Publishing through Steam for Microsoft Windows and Linux in 2015, and OS X in 2016. A Nintendo Switch version was released by Lone Wolf Technology in 2019.
Source: Wikipedia