Review: 4 killer cloud IDEs
JSFiddle is the latest in a long line of emerging Web tools. Many big Web properties, for instance, offer "sandboxes" for playing with their API directly in a Web page. I've debugged Google Maps code several times in a window that Google built for experimenting with it. The browser's included debugger is all that's necessary.
Some developers will see JSFiddle as a tool for experimentation and toys because there's little available for working on the server side of the app. The code can easily call APIs, but you won't build any APIs with it. That would be missing the point. The developers clearly want to encourage more snippets and code that can form the building blocks for Web pages.
Icenium: Mobile dev in the browser
When I said above that developers of native code for mobile devices may be among the last to adopt Web-based tools, I left out a curious hybrid path now popular for apps that don't require squeezing every ounce of performance out of the hardware. Some developers are building their iPhone and Android apps in HTML, then wrapping them in a thin layer of native code. This is a fast way to create apps for different platforms, and it can work well if you're not building cycle-sucking apps such as games.
Telerik's Icenium Mist is a browser-based tool for building mobile apps around the Apache Cordova project, the latest version of a thin layer of device-specific code that was once known only as PhoneGap. Icenium Mist lets you create the apps in your browser and run them in a simulator for the different versions of the iPhone. It's a very quick way to spin up an iPhone app. Icenium Graphite, a companion tool that runs on Windows, handles the build, deployment to your device, and publishing the app to the App Store and Google Play.
Icenium is enough to build many basic apps for your mobile needs. It's not exactly native code, but that power is not necessary for most basic apps. It's a clever remix of the browser environment with the mobile.
Icenium is free through May and $19 per month afterward, with a discount for purchasing a full year in advance.