Alfheim Online
The setting for the second arc of the story, known as ALO for short. All players in the game have wings and are capable of flight. It is a large world, divided into separate 'homelands' for each of its fairy races. In Alfheim's center is a very large tree called the World Tree, and the goal of the game is to reach the top. It implements a skill-based system with players increasing their stats by developing both their combat and non-combat skills. Aincrad, the castle of the first game, is later accessible to ALO players as well.
Gun Gale Online
The setting for the third arc of the story, known as GGO for short. It is a virtual game world with a main focus on guns, although melee weapons like lightsabers and knives also exist. From all the games it is the most competitive one as the money earned there can be exchanged for currency used in the real world, drawing high-tier professional players to make a living from it.
UnderWorld
The setting for the fourth arc of the story. According to Kirito, it is graphically the most realistic of all VRMMOs to date. The flow of time in UW is variable and can be much faster relative to the real world's. Even so, it seems that even Kirito was misled as to the actual rate of UW's time flow, so it is still unknown. However, in the as of yet canon "There is but one ultimate way" side story, the rate is said to be safely up to 1,000 times faster than that of the real world, just like
Accel World's Brain Burst.
.
that was fast heheheh
