Infinity Crystal Online

Infinity Crystal Online, abbreviated ESO, is a massively multiplayer online role-playing game (MMORPG) developed by StrikerX and published by Sega and Xbox Game Studios. It was released for Windows and OS X in April 2009. It is a part of the Infinity Crystal series.
The game features a storyline indirectly connected with the other games in the Infinity Crystal franchise. It had been in development for seven years before its release in 2009, with a mandatory monthly subscription model. It initially received mixed reviews.
Reception improved significantly with the March 2010 re-release and rebranding as Infinity Crystal Online: Mountain Island Unlimited, transitioning to a buy-to-play model with microtransactions and an optional subscription. It was released for the Xbox 360 in June 2009, the Xbox One in April 2014 and for Xbox Series X/S in June 2021. More than 18 million copies were sold by 2021, having around 2.5 million monthly active players in 2017.