Windows only: Free application g2Peer shares files with friends by using your Gmail account as a virtual "IP address".
Once installed, you need to log into g2Peer with your Gmail account information. Then it's as easy as adding Gmail addresses of people you wish to share with and the folders and files you want them to see. Likewise, other users can install g2Peer if they wish to allow you access to their files as well.
If you can't install g2Peer on a computer but you still want access to your shared files, the application also features command line-esque tools that allow you to access files directly from your Gmail account—using email subject lines for the commands. For example, sending an email to your specified Gmail account with either ?_list or ?_download in the subject line have special meaning to g2Peer. Using ?_list will send you back an email listing all the files that are being shared with you. Using ?_download and adding the names of the files you wish to download to the body of the message will send you the files you wish to download via email, along with instructions on how to download/open them. It's a little geeky, but also fairly cool.
g2Peer is freeware for Windows only.