Build a planet. Run its climate.

Pick a geography: Earth, Pangea, other ancient Earths, an aquaplanet, or paint your own continents. Set the sliders: sun, greenhouse, tilt, day length, ocean depth. Each slider shows where Earth's own range ends; stay inside it and the planet is Earth-like, cross it and the planet is Extreme, with its own boards. Lock either division if you want the sliders held to it.

A real climate model (SpeedyWeather) runs 45 simulated years on your planet, in the cloud, about 1.5–3.5 hours. Go do something else; you'll get a notification when it's done. Then read any spot on the globe: its monthly climate, its Köppen class, and a shareable Four Seasons card.

Pick a moment from your planet's own history and run a real weather model (MPAS, 120 km) for a 5, 10 or 15-day forecast: clouds, rain and snow, wind, the jet stream, tropical cyclones. Pick a spot for its 3-hourly meteogram and a shareable TV-style forecast card.

Every valid planet is ranked on leaderboards, gold/silver/bronze. Timed challenges put everyone's planets against one shared clock and a shared prize pool.