Rust Wiki description

Rust is an open world MMO survival game designed by Facepunch Studios. It takes inspiration from games like DayZ, Minecraft, and STALKER. To survive in Rust you may choose to work together with friends and strangers, scavenging for supplies and building giant bases, or go at it alone, killing other players for loot. Rust aims at being a game that gives players the freedom to play the way that they want, and that doesn't involve a hero and bandit system. With Rust, you will have to use your instinct, not a humanity number, to figure out if you can trust people.

Rust is running on the Unity Engine. You can purchase the Rust Alpha on Steam. The game is updated quite frequently - and it's changing a lot.
The game is currently in early alpha. Everything is subject to change. Read through the Frequently Asked Alpha Questions.