OnePlus And Cyanogen Inc. ended their relationship on a sour note last year, leaving the former in a position to start producing its own software. After putting a team together, it began developing ROMs for the OnePlus One independently. Of course, these builds needed a name. So as the company is want to do, it held a contest. The winning name is, without further ado, OxygenOS.
Why this name? OnePlus finds oxygen, the element, to be highly inspirational.