Version 0.7.0 of the googleVis R package has been released, adding a new function for Gantt charts. Gantt charts are helpful to illustrates a project schedule and its dependencies.
Following the Google documentation the project has to be broken down into task IDs, task names, resources, start date, end dates, task duration (in milliseconds), how far the task has been completed (in percent), and finally any dependencies to other tasks IDs.