Early access to Screeps is now available for Windows, OS X, and Linux on Steam, offering first crack as this MMORTS game that relies on actual programming skills to play. Here's a trailer showing off how this works. While this will limit the potential audience of this game, it is an interesting new approach to things, as outlined here:

It is a MMO RTS sandbox game for programmers, wherein the core mechanic is programming your units AI. With all the attributes of a full-fledged strategy game, you control your colony by writing real JavaScript which operate 24/7 in the single persistent world filled by other players on par with you.

Your colony can harvest resources, build units, conquer territory, trade with another colonies. As you conquer more territory, your influence in the game world grows, as well as your abilities to expand your footprint. However, it requires a lot of effort on your part, since multiple players may aim at the same territory.

Screeps is developed for people with programming skills. Unlike some other RTS games, your units in Screeps can react to events without your participation – provided that you have programmed them properly. And, unlike other MMO, you do not have to play Screeps constantly to play well. It is quite enough just to check once in a while to see if everything goes well.