Games like Siege Saga
Games like Siege Saga include Teardown, Garry's Mod, People Playground, Wobbly Life, and Goat Simulator. We matched them by the tags players give Siege Saga on Steam (Casual, Adventure, Indie, Physics, and Sandbox): closest matches first, and among equally close ones the better-known games.

Teardown
Shared: Physics · Destruction · Sandbox

Garry's Mod
Shared: Sandbox · Physics · Casual

People Playground
Shared: Sandbox · Physics · Destruction

Wobbly Life
Shared: Adventure · Sandbox · Casual

Goat Simulator
Shared: Casual · Sandbox · Physics

Human Fall Flat
Shared: Adventure · Physics · Sandbox

Totally Accurate Battle Simulator
Shared: Sandbox · Physics · Indie

Donut County
Shared: Casual · Indie · Physics

Noita
Shared: Physics · Indie · Sandbox

Besiege
Shared: Physics · Sandbox · Destruction

Turbo Dismount™
Shared: Physics · Destruction · Indie

Chained Together
Shared: Adventure · Casual · Indie

BeamNG.drive
Shared: Physics · Destruction · Sandbox

Florence
Shared: Casual · Indie · Adventure

Starbound
Shared: Adventure · Sandbox · Casual

The Scroll of Taiwu : Beyond The Dome
Shared: Sandbox · Indie · Adventure

Flashing Lights - Police, Firefighting, Emergency Services (EMS) Simulator
Shared: Adventure · Physics · Destruction

Just Cause 4 Reloaded
Shared: Adventure · Destruction · Sandbox

Fun with Ragdolls: The Game
Shared: Physics · Sandbox · Indie

How to Fish
Shared: Indie · Adventure · Physics

Terraria
Shared: Sandbox · Adventure · Indie

Slime Rancher
Shared: Adventure · Casual · Sandbox

Pikuniku
Shared: Adventure · Casual · Indie

Kerbal Space Program
Shared: Physics · Sandbox · Indie