Games like Horizon Idle
Games like Horizon Idle include Firestone – Idle Clicker Online RPG, Melvor Idle, Digseum, Loot Loop, and Cookie Clicker. We matched them by the tags players give Horizon Idle on Steam (RPG, Simulation, Auto Battler, Incremental, and Idler): closest matches first, and among equally close ones the better-known games.

Firestone – Idle Clicker Online RPG
Shared: Incremental · Auto Battler · Idler

Melvor Idle
Shared: RPG · Idler · 2D

Digseum
Shared: Incremental · Simulation · Idler

Loot Loop
Shared: Simulation · Incremental · Idler

Cookie Clicker
Shared: Incremental · Idler · Economy

Tower Wizard
Shared: Incremental · Idler · 2D

Fortune Mill
Shared: Incremental · Idler · Simulation

(the) Gnorp Apologue
Shared: Incremental · Idler · Economy

Nodebuster
Shared: Incremental · Simulation · Idler

Scritchy Scratchy
Shared: Incremental · Idler · Simulation

Magic Research 2
Shared: Auto Battler · RPG · Idler

Click and Conquer
Shared: Simulation · Incremental · Idler

Lootun
Shared: RPG · Auto Battler · Idler

Dragon Cliff
Shared: RPG · Idler · Incremental

Keep on Mining!
Shared: Incremental · Idler · Mining

Your Chronicle
Shared: RPG · Idler · Incremental

Starvester
Shared: Incremental · Idler · Simulation

A Game About Feeding A Black Hole
Shared: Incremental · Simulation · Idler

Orc Incremental
Shared: Auto Battler · RPG · Idler

Shelldiver
Shared: Incremental · Idler · Simulation

Factory Town Idle
Shared: Incremental · Idler · Minimalist

Gamblers Table
Shared: Incremental · Minimalist · Idler

Endless Sky
Shared: Simulation · RPG · Sci-fi

Journey to Incrementalia
Shared: Auto Battler · Incremental · RPG