Backpack is by far the best online application I've ever paid for. I use it on a daily basis for my work as a freelance journalist. For me it's a mixture of notepad, storage and organisational tool. Also, I use it all the time to collaborate with partners on ideas and projects. The writeboard function (which is free by the way) is perfect for letting sources and customers read and edit texts, and it let's keep track of all the changes. Highly recommended!