In the days before the OASIS, massively multiplayer online games (MMOs) were among the first shared synthetic environments. They allowed thousands of players to simultaneously coexist inside a simulated world, which they connected to via the Internet. The overall size of these environments was relatively small, usually just a single world, or a dozen or so small planets. MMO players could only see these online environments through a small two-dimensional window—their desktop computer monitor—and they could only interact with it by using keyboards, mice, and other crude input devices.