It reminds me a lot of a project I am working on, modul.io [1].

- Everything is programmable, including the UI and the appearance of your modul

- A modul can send and receive messages with the moduls around it

- You start with a predefined and ready to use modul

- Offline support: your modul continues to live on the server when you are not connected

There is no game mechanics at all though, our goal is to create everything using moduls (games, entities composed of multiple moduls, tools…).

Planned features:

- A REST API to do everything remotely

- Code sharing using library packs

I can't wait to see how Screeps work!