.flow is one of the most well-known fangames of the original Yume Nikki, made by lol. It's one of the darker spin-offs infamous for its eerie atmosphere and copious amounts of body horror and hospital imagery, centering around a girl named Sabitsuki (さびつき) as she enters her PC dreamworld to explore her mind and collect effects.
.flow is one of the more traditional fangames that stays true to the gameplay elements of the original. Effects are collected in a gloomy, sublime dreamscape and the user is left to interpret the events and lack of explicit storyline. The only differences that seem to set this game apart from Yume Nikki is the more concrete subject matter (the deeper aspects of the landscape seem to have a more pristine resemblance to human body parts, where as Nikki's environment requires more interpretive thinking to analyze) and the inclusion of three endings instead of one.
The main plot of the game is similar to the original Yume Nikki's, in that it's a sandbox game with very few exploration restrictions. You must collect the twenty-five effects to unlock two of the three endings and three boxes to achieve the third.
