Fly

Overview

Fly is a multiplayer 3D flight simulator that runs entirely in the browser, built by Pieter Levels (@levelsio) using Cursor and Three.js. Pieter shipped the first playable version in around three hours, posted it on X, and watched it explode into a cultural moment that effectively kicked off the "vibe-coded game" era of 2025.

What It Does

Players load fly.pieter.com and immediately spawn into a low-poly 3D world where they can pilot a small plane, fly alongside other live players, and explore shared airspace. There is no install, no account creation, and no client to download — the entire experience runs in WebGL via Three.js. Over time the game accumulated branded in-world objects, sponsored landmarks, and ad placements that turned a weekend hack into a serious revenue engine.

How It Was Built

Pieter has been openly documenting the build on X. The stack is Three.js for rendering and multiplayer state in the browser, glued together with code generated through Cursor. Pieter has emphasized that he is not a games engineer by background — the prototype came together by iterating with the AI in Cursor against a Three.js scaffold, asking it to add planes, networking, collisions, and game-feel tweaks one at a time.

Traction

• Built in roughly 3 hours of initial work
• Peaked at over $100K/month in revenue from in-game ads and branded objects
• Triggered a wave of imitator vibe-coded browser games throughout 2025
• Frequently cited as the canonical example of "vibe coding" by both Cursor and the broader indie hacker community

Why It Matters

Fly proved that a single solo developer using an AI coding tool could ship a multiplayer 3D game in an afternoon and turn it into a six-figure-MRR business. It collapsed the gap between "I had an idea" and "people are paying me for it" in a way that reshaped what indie game development looks like.