Google just introduced a new tool to allow third-party applications that run in an HTML iFrame. It's a fairly simple concept, but creativity tools (by definition) extend what can be done on a platform--and as seen with Facebook, it can build popularity for a platform overall.
Already, Youtube.com/create has a variety of different tools for creating video.
In order to list your application on the platform, you will need some accompanying meta information, such as: name of application, a description, a 20x120 icon, a hosted (Youtube) tutorial video--all of which will be used to promote your tool.
The application must include Google federated login using OpenID. It must be able to post the created video to the Youtube website. The app must be branded so users understand that the video is going to a third-party application, and not directly to Youtube itself. It must not show ads directly within the iFrame.