SDK

An SDK (Software Development Kit) is a set of tools which allows programmers to create applications for specific software packages. Such tools often include debugging tools, libraries, 'help' documents and other such common utilities. These tools are usually presented in an IDE (Integrated Development Environment). Game Maker is considered an SDK for YoYogames. Many SDKs are free of charge, but have fees attached to publishing created works.

Free SDKs

 * IPhone SDK (But, loading an application onto the devices is only possible after paying a iPhone Developer Program fee.)
 * Microsoft Windows SDK
 * Java Development Kit (since 17th November 2006)

Commercial SDKs

 * Adobe Flex SDK (free trial)
 * Qt (free 30 day trial)
 * Source SDK (from Valve)