Javascript HTML5 web applications would be pretty easy to support being loaded into the in-game web-browser and it's one of the most common / easy to pickup languages making it a perfect option for creating rich and fun new software apps that could be sold on an in-game App Store. This creates the opportunity for players with that kind of background to build out new features into the game that would otherwise take a long time for the dev team to get around to and also gives them a way to earn in game currency. Expansions - API to interact with other in game systems like the stock market, bank, shops, factories, phone GPS, security systems etc. - Live linking to real externally hosted (Approved) web applications further increasing immersion and crossing the bridge between in game and reality. Essentially I would think it'd be neat to have an in-game editor for building these, but lets face it, if people are allowed to create applications like this, most are going to use an external setup and just spit out a minified javascript bundle, copy the code and paste into the in game editor to spin up their web applications... which isn't a bad thing really as it saves the hassle of building a fancy IDE in game.