Yume 2kki (ゆめ2っき)

Overview
Yume 2kki (ゆめ2っき) (Yume Nikki, literally Dream Diary, but also a pun on the original game's title -- に, or "ni," means 2) is the original fangame that started it all. It is a large collaboration project from 2ch users and thus features a wide variety of worlds, effects, and ideas.

Gameplay
Just like the original game, there is no overarching plot and the only goal is to explore and collect all of the effects.

A unique feature of Yume 2kki is the inclusion of collectible wallpapers unlocked by reaching certain areas or activating certain events. These can be found on Urotsuki's real world PC and serve as a large side-quest for the game. Collecting 195 of the 206 wallpapers unlocks one of the game's four endings.

You can also collect, then listen to the in-game music, as well as menu themes, who are scattered in the dream world in the shape of eggs.

Plot
Due to the vast and many, many worlds of Yume 2kki, plus the four main endings, multiple theories have been made, and it is really up to the player on how they choose to interpret it.

Effects
Yume 2kki has a massive 34 effects, something unique about the game is the ability to mix effects, such as Bike + Wolf.

Each of these effects have a particular use that can be found by traveling in the dream worlds.

Effect Mixes
For more information on Yume 2kki's effects and where to find them, please see the Yume 2kki's Wiki.