Xonox was a a third party producer of Atari 2600 games. They made double ended games for the most part. That is, games that you could stick in your Atari upside down to get a different game altogether.
Chuck Norris Superkicks
Super Kung Fu
Tomarc the Barbarian
These games were all available by themselves, and in double ended multicart
s with other games on this same list.