This tool is a bit old, but I guess it’s worth to mention it
It’s about synchronizing files across many computers, using BitTorrent. You can think on this as a DropBox alternative, with the following differences:
1-No limits, the limit will be the space in hard drive. As of now, I have more than 40GB synchronized within all my computers (Music, personal documents and part of the /etc/ directories)
2-It does not need the cloud. If you have computers in a LAN and no access to the internet, they will sync internally at amazing speed.
3-BitTorrent based, so as soon as a computer has a part of the file, it can become a source for that part of the file in the network.
4-Again, it does not need the cloud. The files are never stored in a remote third-party service as DropBox, UbuntuOne, Google Drive and so on.
5-Keeps up to 30 revisions of the files
It is not open source, but the application is completely free to download and use. The free software foundation set this project as a priority to make it open source. And in the last month the developers made public the API, allowing developers to build the GUIs to manage the service, available at http://www.bittorrent.com/sync/developers