Games like Summer Nightmare
Games like Summer Nightmare include Milk inside a bag of milk inside a bag of milk, NOeSIS01_诉说谎言记忆物语, Tiny Bunny: Prologue, Raging Loop, and 妄想症:Deliver Me. We matched them by the tags players give Summer Nightmare on Steam (Free to Play, Visual Novel, Anime, Horror, and Gore): closest matches first, and among equally close ones the better-known games.

Milk inside a bag of milk inside a bag of milk
Shared: Visual Novel · Horror · Psychological Horror

NOeSIS01_诉说谎言记忆物语
Shared: Visual Novel · Horror · Anime

Tiny Bunny: Prologue
Shared: Visual Novel · Horror · Free to Play

Raging Loop
Shared: Visual Novel · Adventure · Indie

妄想症:Deliver Me
Shared: Visual Novel · Indie · Anime

Tiny Bunny
Shared: Visual Novel · Horror · Gore

Poppy Playtime
Shared: Free to Play · Horror · Psychological Horror

Doki Doki Literature Club Plus!
Shared: Visual Novel · Anime · Psychological Horror

Return to Shironagasu Island
Shared: Visual Novel · Horror · Anime

The Song of Saya
Shared: Visual Novel · Gore · Horror

Voices from the Sea
Shared: Free to Play · Visual Novel · Anime

Danganronpa: Trigger Happy Havoc
Shared: Visual Novel · Anime · Horror

Corpse Party
Shared: Anime · Horror · Visual Novel

The Murder of Sonic the Hedgehog
Shared: Free to Play · Visual Novel · Casual

Tiny Snow
Shared: Visual Novel · Anime · Casual

Tales of the Black Forest
Shared: Horror · Anime · Visual Novel

YOU and ME and HER: A Love Story
Shared: Visual Novel · Anime · Psychological Horror

Fox Hime
Shared: Visual Novel · Anime · Casual

Fox Hime Zero
Shared: Visual Novel · Anime · Casual

VRChat
Shared: Free to Play · Anime · Casual

Dark Deception
Shared: Free to Play · Horror · Psychological Horror

The Letter - Horror Visual Novel
Shared: Visual Novel · Horror · Indie

An alt girl for skoof
Shared: Visual Novel · Anime · Psychological Horror

月影魅像-解放之羽-
Shared: Visual Novel · Anime · Adventure