Trello is an excellent site for organizing and collaborating on projects w/ others. This is done through the use of on online board (similar to a whiteboard) that is filled up w/ tasks. These tasks are arranged in cards and can be used in real-time w/ others. These cards can have multimedia content such as audio and video embedded into the card. This is ideal for working on projects and having others see view/collaborating. Everything is backed up and stored online and very easy to use.
I recommend checking out Trello by clicking here!!
For a much more detailed review check out Vicki Windman's T & L review by clicking here.