Hello,
I have created a very small (ca 45 MB in size) live CD called 4MDoom. It's a mini Linux distro that boots directly to the Freedoom game.
Detailed description:
http://4mlinux.blogspot.com/2015/01/4mdoom.html
http://linux.softpedia.com/blog/4MDoom-11-0-BETA-Is-a-Distro-That-Boots-Only-into-a-Doom-Type-Game-470462.shtml
Hoping somebody will find it interesting :-)