Games like Aviassembly
Games like Aviassembly include Kerbal Space Program, Scrap Mechanic, Kerbal Space Program 2, Stormworks: Build and Rescue, and Brick Rigs. We matched them by the tags players give Aviassembly on Steam (Building, Physics, Flight, Sandbox, and Transportation): closest matches first, and among equally close ones the better-known games.

Kerbal Space Program
Shared: Physics · Sandbox · Building

Scrap Mechanic
Shared: Building · Sandbox · Physics

Kerbal Space Program 2
Shared: Building · Sandbox · Physics

Stormworks: Build and Rescue
Shared: Building · Sandbox · Physics

Brick Rigs
Shared: Building · Sandbox · Physics

Space Engineers
Shared: Building · Sandbox · Physics

SimplePlanes
Shared: Flight · Physics · Building

The Forest
Shared: Building · Crafting · Open World

Besiege
Shared: Physics · Sandbox · Building

Medieval Engineers
Shared: Building · Physics · Sandbox

Garry's Mod
Shared: Sandbox · Physics · Building

BeamNG.drive
Shared: Physics · Simulation · Sandbox

Terraria
Shared: Sandbox · Building · Crafting

Satisfactory
Shared: Building · Crafting · Open World

TerraTech
Shared: Building · Sandbox · Open World

People Playground
Shared: Physics · Sandbox · Building

Spaceflight Simulator
Shared: Sandbox · Exploration · Simulation

Rust
Shared: Building · Crafting · Sandbox

Conan Exiles Enhanced
Shared: Building · Open World · Sandbox

Space Engineers 2
Shared: Building · Sandbox · Physics

Avorion
Shared: Building · Sandbox · Exploration

Core Keeper
Shared: Exploration · Open World · Sandbox

Totally Accurate Battle Simulator
Shared: Sandbox · Physics · Simulation

Fireworks Mania - An Explosive Simulator
Shared: Building · Sandbox · Physics