Flow (stylized as flOw) is an indie video game created by Jenova Chen and Nicholas Clark. Originally released as a free Flash game in 2006 to accompany Chen's master's thesis, it was reworked into a 2007 PlayStation 3 game by his development studio, Thatgamecompany. SuperVillain Studios released a PlayStation Portable version of the game in 2008, and PlayStation 4 and PlayStation Vita versions in 2013. In Flow, the player navigates a series of two-dimensional (2D) planes with an aquatic microorganism that evolves by consuming other microorganisms. The game's design is based on Chen's research into dynamic difficulty adjustment at the University of Southern California's Interactive Media Division, and on psychologist Mihaly Csikszentmihalyi's theoretical concept of mental immersion or flow.
The Flash version of Flow received 100,000 downloads within its first two weeks of release, and had been played over 3.5 million times by 2008. Its PlayStation 3 re-release was the most downloaded game on the PlayStation Network in 2007, and won the Best Downloadable Game award at the 2008 Game Developers Choice Awards. It was nominated for awards by the Academy of Interactive Arts & Sciences and the British Academy of Film and Television Arts (BAFTA). Reviewers praised Flow's visual and audio appeal, but noted the simplicity of its gameplay; several considered it to be more of an art piece than a game.
In Flow, the player guides a small, multi-segmented worm- or snake-like creature through an aquatic environment. There are no menus or guidelines; the game begins immediately. The game world, which is viewed from a top-down perspective, consists of two-dimensional planes stacked vertically upon each other. A blurred version of the layer below appears in the background of each plane. Planes contain organisms of varying sizes; the player's creature automatically attempts to consume them when they are nearby. The majority of these creatures are non-confrontational, and are composed of cells that increase the number of segments in the player's creature when eaten. All planes, except for the highest and lowest, contain two specially colored organisms that move the player's creature up or down one plane when touched.
Certain planes feature aggressive, multi-segmented creatures that perish when all of their segments are eaten by the player's creature; however, they can eat segments of the player's creature to regrow their own. These creatures release many cells upon death, which can restore the health of the player's creature, temporarily increase the size of its mouth, or cause it to sprout decorative protrusions. Players are not required to eat these or any other organisms; they may travel to higher or lower planes at any time. Being defeated by aggressive creatures does not result in death, but causes the player's creature to float to a higher plane. In the Flash version, the player can replay the game with a jellyfish-like organism by defeating an aggressive creature on the bottom plane. If the player reaches the bottom again, the creature there is their original worm-like creature, and defeating it starts the game over as that organism.