Taskworld allows you to create a task in multiple project locations. This is especially handy when you want to organize certain tasks in your own private project.
Click on the task to access its properties.
Click on "+" icon next to Location tab.
Select Project and Tasklist where you'd like to add the task.
Click on Add New Location.
You can remove a task location by clicking on "X" icon next to it.
Note: Adding Tasks in Multiple Locations only works in a Public Project and a Private Project with a "Full Access" permission settings.