Doors Horizon is an operating system created by Micro Hard and Soft as a replacement for Doors XP, but failed because of bad reviews. G uses it as his test computer software, even though he thinks it isn't very good. It was rated so bad that a lot of people don't even notice its existence until it was leaked in late 2007. It is currently unavailable as the developers are focusing on Doors 7. The estimate of its usage was only 2 % of the Doors market (only 500 users) according to scientists and the Time Agency seeing its decline in late 2011.