Screeps

Screeps means “scripting creeps.” It’s an open-source sandbox MMO RTS game for programmers, wherein the core mechanic is programming your units’ AI. You control your colony by writing JavaScript which operate 24/7 in the single persistent real-time world filled by other players on par with you. 

Scripting as Gameplay

• Real programming, not just pseudocode. You can use libs from real projects.
• Use JavaScript or any transpiled language (e.g. TypeScript).
• Docs and game API of a full-fledged platform.
• Programmable Persistent World
• Huge persistent world consisting of 40,000 connected game rooms.
• 30-server cluster (120 CPU cores) processing player scripts using Node.js.
• Programmable world living a continuous life 24/7 in real-time even when you're offline.
• Open Source Sandbox
• Engine released on GitHub as an open and moddable program platform.
• You can change any aspect of game objects' behavior.
• The sandbox concept doesn't imply any goal or storyline. You just code for fun in a shared game space alongside other players.