Y Combinator funded AppJet is an online programming tool for building simple web apps. Founded by former MIT students, AppJet intends to simplify the process of writing web applications. The applications are programmed on a web based text editor in the simple but powerful JavaScript programming language. JavaScript is used on both the server and client side. They’ve included several bundles of code libraries for databases and more importantly interfacing with the Facebook API. In order to efficiently host users’ applications, AppJet has developed their own application virtualization system. The system allocates processor time to active applications and cuts off greedy ones after running an alloted number of compiled lines of code to prevent abuse.

AppJet as a dev platform seems no longer to be active. There are some legacy downloads available, however.