I don't know if if I can fully express how profoundly important this game was to me, I started playing it at a pretty dark time in my life, and for a little bit it was a great source of comfort for me. There is a lot to say about it, but ultimately it's a game that is best experienced on your own.
Yume Nikki, or "Dream Diary" in english, is an exploration game, made inside of the game engine RPGmaker. This is a really odd use of RPGmaker, but was prolific enough in it's community to spawn several similarly themed games. In example .flow and Yume 2kki. The creator of this game's name is KIKIYAMA, and very little is known about them, or if they are even alive anymore.
In this game, you traverse the many dream worlds of the main character, Madotsuki. She's a troubled hikikomori, and doesn't leave here room (she just shakes her head if you try). The dream worlds are surreal and unique each in their own way, inhabited by strange creatures, and interconnected by either the original set of doors you encounter, or strange passage ways. I think some of my personal favorite worlds are The Checkered Tile Path, FC Dungeon, Mars, and the Docks, but it's so hard to choose. The goal of the game is to collect all the "Effect" which augment Madotsuki in some way. Some places in the game require particular effects to get to. When you have collected them all you are suppose to drop them all inside the "Nexus" (the room with all the doors). All the rooms are set to very simplistic, but devastatingly effective and immersive looping soundtracks. This game also doesn't feature any dialog, it's just you and your thoughts. There is so so much to see and experience.
There was also a remake of this game titled YUMENIKKI -Dream Diary-, it's kinda like a 3d re-imagining of the environments and ideas in the original Yume Nikki. I haven't completely finished the game yet, but I think it's seems kinda interesting so far. A lot of people seem to totally hate it though, and I agree it doesn't completely hold up to the original, but I think thought of as a fan project it has it's own appeal.
^ Pics Above ^ : Falling out of bed after flying with the witch's broom in the dream world
It's kind of a funny story, I found this game much much earlier than when I had really gotten into it. I was looking for neat indie games at the time and had downloaded ii to try out. I started right off and got stuck in the NASU game, and didn't know you had to hold ESC to get out of it as apposed to just pressing it. I assumed the game was completely bugged out and unfinished (as were a lot of indie games I tried were at the time), closed it and deleted it. Oh how I was wrong to think that lmao.
I found the atmosphere and subject matter from the game to be extremely relatable, and I hope you enjoy it as much as I did (and still am).
Here are some associated links:
Yume Nikki Download (Uboachan english translation)
This is the version I prefer
Yume Nikki's Fandom Wiki
There are Walk-throughs, effect descriptions, fan theories, etc here
Image Board themed around Yume Nikki
Uboachan Fandom Wiki
More info on the game, it's creator, and history about the Uboachan site
Yume Nikki's Steam page
It's free here ofc, and has a few quality of life fixes / different translation, personally I like the Uboachan translation more
Yume Nikki -DREAM DIARY- Steam page
The 3D remake of Yume Nikki