.flow
.Flow is one of the most popular fangames to the original Yume Nikki, lol. It's one of the darker spin-offs, known for its eerie atmosphere and plenty of body horror and hospital imagery. It centers on a girl named Sabitsuki (さびつき) who enters her PC dream world 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. The effects are collected in a dark, sublime dream world and it is left to the player to interpret the events, since there is no explicit plot. The only differences that seem to distinguish this game from Yume Nikki are the more concrete subject matter (the deeper aspects of the landscape seem to have a more primal resemblance to human body parts, while 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 that of Yume Nikki, in that it is a sandbox game with very few exploration restrictions. You'll have to collect the twenty-five effects to unlock two of the three endings, and three boxes to achieve the third one.
Story
Similar to Yume Nikki, very little is known about the main character, a girl named Sabitsuki. Similar to Madotsuki, the protagonist of Yume Nikki, Sabitsuki lives in an apartment with a bed, a single game console, a television, and most importantly, a computer that she uses to enter a state known as "flow." While in flow, Sabitsuki (and the player) enters a surreal, immersive reality connected to her psyche that she can explore to find 25 "effects." Who exactly Sabitsuki is, what she has been through, and what world she lives in is up to the player to interpret based on what he/she sees and experiences in the flow.