Games like Letters - a written adventure
Games like Letters - a written adventure include Undertale, OneShot, Carto, Detroit: Become Human, and Volcano Princess. We matched them by the tags players give Letters - a written adventure on Steam (Choices Matter, Hand-drawn, Female Protagonist, Multiple Endings, and Colorful): closest matches first, and among equally close ones the better-known games.

Undertale
Shared: Choices Matter · Multiple Endings · Story Rich

OneShot
Shared: Story Rich · Choices Matter · Cute

Carto
Shared: Hand-drawn · Cute · Female Protagonist

Detroit: Become Human
Shared: Choices Matter · Multiple Endings · Story Rich

Volcano Princess
Shared: Choices Matter · Multiple Endings · Female Protagonist

GRIS
Shared: Female Protagonist · Hand-drawn · Atmospheric

Road 96
Shared: Choices Matter · Colorful · Multiple Endings

OMORI
Shared: Story Rich · Hand-drawn · Multiple Endings

The Henry Stickmin Collection
Shared: Multiple Endings · Choices Matter · Funny

Life is Strange: Before the Storm
Shared: Choices Matter · Female Protagonist · Story Rich

Far Away
Shared: Choices Matter · Female Protagonist · Story Rich

Oxenfree
Shared: Choices Matter · Female Protagonist · Story Rich

Life is Strange: True Colors
Shared: Choices Matter · Female Protagonist · Multiple Endings

Little Misfortune
Shared: Choices Matter · Story Rich · Female Protagonist

Slime Rancher
Shared: Cute · Colorful · Funny

A Hat in Time
Shared: Cute · Female Protagonist · Funny

The Coffin of Andy and Leyley
Shared: Multiple Endings · Choices Matter · Story Rich

LoveChoice
Shared: Choices Matter · Multiple Endings · Story Rich

Life is Strange Remastered
Shared: Choices Matter · Female Protagonist · Multiple Endings

Magical Princess
Shared: Choices Matter · Multiple Endings · Female Protagonist

Road to Empress I
Shared: Choices Matter · Female Protagonist · Story Rich

Lost in Play
Shared: Hand-drawn · Colorful · Funny

Lost Records: Bloom & Rage
Shared: Choices Matter · Female Protagonist · Multiple Endings

The Witcher 3: Wild Hunt — Remastered
Shared: Story Rich · Choices Matter · Atmospheric