Games like Onset
Games like Onset include Mount & Blade II: Bannerlord, Last Oasis, Rust, The Isle, and Stardew Valley. We matched them by the tags players give Onset on Steam (RPG, Massively Multiplayer, Simulation, Action, and Indie): closest matches first, and among equally close ones the better-known games.

Mount & Blade II: Bannerlord
Shared: RPG · Open World · Multiplayer

Last Oasis
Shared: Massively Multiplayer · RPG · Action

Rust
Shared: Open World · Multiplayer · Sandbox

The Isle
Shared: Simulation · Open World · Massively Multiplayer

Stardew Valley
Shared: RPG · Simulation · Multiplayer

Once Human
Shared: Open World · Action · Multiplayer

Mount & Blade: Warband
Shared: RPG · Open World · Action

Gloria Victis: Medieval MMORPG
Shared: Massively Multiplayer · RPG · Action

Kenshi
Shared: RPG · Open World · Sandbox

Conan Exiles Enhanced
Shared: Open World · RPG · Massively Multiplayer

EmergeNYC
Shared: Simulation · Action · Open World

Feed and Grow: Fish
Shared: Simulation · Action · Multiplayer

Dark and Light
Shared: Massively Multiplayer · RPG · Open World

Wobbly Life
Shared: Simulation · Open World · Multiplayer

Albion Online
Shared: Massively Multiplayer · RPG · Open World

Project Zomboid
Shared: Open World · Multiplayer · Sandbox

The Elder Scrolls Online - Standard Edition
Shared: RPG · Open World · Massively Multiplayer

Elite Dangerous
Shared: Simulation · Open World · Massively Multiplayer

Beasts of Bermuda
Shared: Simulation · Massively Multiplayer · Open World

Miscreated
Shared: Open World · Massively Multiplayer · Multiplayer

The Scroll of Taiwu : Beyond The Dome
Shared: RPG · Open World · Sandbox

Tower Unite
Shared: Massively Multiplayer · Multiplayer · Open World

Don't Starve Together
Shared: Multiplayer · Open World · RPG

Monster Hunter: World
Shared: RPG · Action · Multiplayer