Winding (XO) is the main computers Operating System in Angel Beats!. Its logo is depicted of a red, green, blue, and yellow spiral.
It can be speculated that the Winding computers only exist inside the Afterlife as no such company actually exists in the real world, along with the fact it is probably the only Operating System that can execute Angel Player.
- Winding is a reference to the most popular computers Operating System in the world, Windows.
- Winding's publisher, MacroSoft, is a reference to Microsoft, being that "macro" is the antonym of "micro".
- The Winding boot-up screen is similar to the boot-up screen of that of Windows XP. XO is probably used because many fast typers usually hit the "O" key for "P".