Each application and its associated developer key are limited to one product.

If you would like to access the APIs for multiple products then you will create multiple applications, each application being specific to one of the products you wish to access. For example a web application that uses both GoToMeeting and GoToTraining might create applications Meeting-integration and Training-integration. When making calls to the product APIs, the application would need to make sure it uses the correct developer key for the specific calls.

Please note that OAuth authorization process is specific to an application. In the example above a user would need to authorize your application for access to their GoToMeeting account as well as their GoToTraining account.