Games like Afterthought
Games like Afterthought include Celeste, Geometry Dash, Super Meat Boy, Hollow Knight: Silksong, and Jump King. We matched them by the tags players give Afterthought on Steam (Precision Platformer, Difficult, Indie, Atmospheric, and Singleplayer): closest matches first, and among equally close ones the better-known games.

Celeste
Shared: Precision Platformer · Difficult · Indie

Geometry Dash
Shared: Difficult · Precision Platformer · Singleplayer

Super Meat Boy
Shared: Precision Platformer · Difficult · Indie

Hollow Knight: Silksong
Shared: Difficult · Indie · Singleplayer

Jump King
Shared: Difficult · Precision Platformer · Indie

Hollow Knight
Shared: Difficult · Indie · Singleplayer

A Dance of Fire and Ice
Shared: Difficult · Indie · Singleplayer

N++ (NPLUSPLUS)
Shared: Precision Platformer · Difficult · Action

Rain World
Shared: Difficult · Atmospheric · Indie

Getting Over It with Bennett Foddy
Shared: Difficult · Singleplayer · Indie

Super Meat Boy Forever
Shared: Difficult · Indie · Precision Platformer

SANABI
Shared: Action · Indie · Singleplayer

The End Is Nigh
Shared: Precision Platformer · Indie · Difficult

VVVVVV
Shared: Precision Platformer · Indie · Difficult

Planet of Lana
Shared: Action · Atmospheric · Singleplayer

Electronic Super Joy
Shared: Indie · Difficult · Precision Platformer

Cairn
Shared: Indie · Difficult · Singleplayer

Downwell
Shared: Precision Platformer · Indie · Difficult

Hyper Light Drifter
Shared: Indie · Atmospheric · Difficult

Clustertruck
Shared: Action · Parkour · Singleplayer

Nine Sols
Shared: Difficult · Indie · Action

Super Hexagon
Shared: Difficult · Indie · Singleplayer

Dustforce DX
Shared: Precision Platformer · Indie · Difficult

Ambidextro
Shared: Precision Platformer · Indie · Action