There are many different types of mobile massively multiplayer online (MMO) games, from titles that are geared towards casual gaming, to others that are a good fit for the traditional market. The earliest mobile MMOs were very limited in both gameplay and graphics, but modern mobile devices are capable of offering a wider range of experiences. Some mobile MMOs are based around casual gaming hubs that function as online communities, allowing people to compete in a variety of different games that tend to be relatively short and simple. Other mobile games have more in common with traditional MMOs, and there are even massively multiplayer online roleplaying games (MMORPGs) available for phones and tablet devices.
The term, "massively multiplayer online," refers to a class of games that are designed to allow a large number of people to interact at once, often in some type of persistent world. That essentially means that the game world continues to operate even after people have logged out of it. These types of games have existed on proprietary online platforms since the 1980s, though even earlier examples were played on University timeshare systems. Many early MMOs were played on personal computers (PCs), though console-based MMOs were introduced along with the availability of Internet connectivity for those systems. Mobile MMOs became possible later on with increases in processing power, display capabilities, and the Internet data transfer speeds of cellular phones.
Mobile MMOs can be broken into the two basic categories of casual and traditional games, though there is a great deal of ongoing innovation in this area of gaming. Some casual mobile MMOs are based around a single game that can be picked up and played for a short period of time. Others are based around community hubs, where players can come together and play a wide variety of different casual games. Some of these casual MMOs are browser-based, while others require the download of an app.
There are also a number of mobile MMOs that have more in common with traditional PC-based massively multiplayer games. Some of these games are actually ported versions of PC games, while others are essentially clones that are meant to copy the look and functionality of successful PC MMOs. The earliest mobile MMOs were mobile versions of PC-based MMORPGs, though the graphics and gameplay were typically simplified. Modern cellular phones and tablet computers are capable of producing graphics and gameplay that are much closer to levels expected out of PC-based MMORPGs.
Another category of MMO that is impossible on other platforms makes use of the unique feature set presented by the cellular phone platform. Some of these MMOs use systems similar to geocaching, where the gameplay is dictated or altered by the player's physical location. These MMOs can allow people in the same area to compete to locate in-game objects that are tied to coordinates in the real world.