Google announced the ChromeCast last summer alongside the 2013 Nexus 7 and Jelly Bean 4.3, but until now it has lacked 2 crucial things that stopped it becoming much of a success. Firstly, there aren't enough apps that support it, and secondly it was only released in America. Now Google has fixed one of those problems by allowing developers to create apps with support for ChromeCast.
Technically, developers could always create ChromeCast apps, but the process was long and complex. Today's announcement allows developers to are ChromeCast support easily, using the newly released ChromeCast SDK. This is great news for users as it means that each soon the number or ChromeCast enabled apps will skyrocket. The current list of ChromeCast enabled apps can be found here, but it's not a very long list and includes YouTube and Google Play services like Music. By releasing the SDK to developers, supported apps will start appearing all over the place. If you are an app developer, check here to find a detailed description of what you need to do to get your app into the ChromeCast party.