Games like Boulder Smash
Games like Boulder Smash include Vampire Survivors, Haste, Megabonk, Super Hexagon, and Zup!. We matched them by the tags players give Boulder Smash on Steam (Casual, Fast-Paced, Physics, Arcade, and Action): closest matches first, and among equally close ones the better-known games.

Vampire Survivors
Shared: Action Roguelike · Casual · Roguelite

Haste
Shared: Fast-Paced · Action · Roguelite

Megabonk
Shared: Action Roguelike · Action · Roguelite

Super Hexagon
Shared: Fast-Paced · Arcade · Action

Zup!
Shared: Casual · Fast-Paced · Physics

Zup! S
Shared: Casual · Physics · Fast-Paced

Marble It Up! Ultra
Shared: Fast-Paced · Physics · Arcade

Spin Rhythm XD
Shared: Casual · Action · Arcade

Crab Champions
Shared: Action Roguelike · Arcade · Soundtrack

Hades
Shared: Action Roguelike · Action · Roguelite

Superflight
Shared: Casual · Action · Physics

Zup! 2
Shared: Casual · Fast-Paced · Physics

One Finger Death Punch
Shared: Fast-Paced · Action · Casual

Zup! 3
Shared: Casual · Fast-Paced · Physics

Project Lazarus
Shared: Casual · Action · Action Roguelike

Timberman
Shared: Casual · Action · Arcade

Zup! 8
Shared: Casual · Fast-Paced · Physics

Gang Beasts
Shared: Physics · Casual · Action

Post Void
Shared: Fast-Paced · Action Roguelike · Action

Zup! F
Shared: Casual · Fast-Paced · Physics

Orbt XL
Shared: Arcade · Casual · Action

Planes, Bullets and Vodka
Shared: Casual · Action · Arcade

BALL x PIT
Shared: Action · Arcade · Action Roguelike

Garry's Mod
Shared: Physics · Casual · Singleplayer