GQueues is a powerful GTD task manager that interfaces very well with Google/GApps. They do not have an API however their Google Calendar Integration works very well and allows for task management through Google Calendar that leverages the strengths of GQueues. One simple implementation for this in BusinessCalendar could be to allow a setting to designate a calendar as a "tasks" calendar. These events then appear in tasks areas of BusinessCalendar and simply relies upon the integration between Google Calendar and GQueues to create and sync tasks but then displays these in the task areas of Business Calendar. Seems like it might be a simple way to leverage this tool and also an opportunity as this would be the only 3rd party app to integrate GQueues as tasks in a calendering app. Annotated this idea in the screenshot below.
https://www.dropbox.com/s/lbxmjymluht88of/Screenshots_2015-01-22-08-33-16.png?dl=0