Do you remember GDrive? It had come up some time back, where users could use their GMail accounts like a virtual storage drive. I am not sure as to why it disappeared, possibly due to Google Docs and copyright issues, but it was great to have a online storage for your crucial documents. If I am going home and I want to take some files with me, why bother carrying them in a pen-drive when you can always have it online and access them anytime you want as long as you have internet.
Well, Dropbox does exactly that! You get a 2GB free account, from which you can version and collaborate documents. A good collaborative tool as any. There are a lot of such tools, but I really like the ease with which a newbie can start using this tool. Will try it as a tool within the office and post on this further.
Addendum
This is my application of the Dropbox idea. I have backed up my entire workspace (documents, mail, setups I need, etc) in one dropbox. And wherever I go I have my workspace online! No need for machines, laptops, pen drives whatever. Give me a new machine and all I have to do is install this nifty little application and voila! All my workspace documents will be synced with me in no time.