For a project, I have been asked to put a complete Facebook application inside the timeline. However, I cannot find any information about this in the Facebook reference. Does an
I believe your client wants to use the new Add To TimeLine feature. This provides another introduction from user perspective.
As an example, this image shows Spotify, NetFlix and Nike app implementations of the new feature on the timeline:
You can implement a basic "add to timeline" functionality using the JavaScript SDK although API documentation is limited.
You can also create customized app contents and aggregate contents ("movies watched this month on Netflix") for the Timeline by integrating your app with the Open Graph. Facebook has this introductory tutorial.