Keystrokes :.

7z is a compressed archive file format that supports several data compression methods, featuring hight compression ratio, encryption and support for large files (up to 16 exabytes). Although it does not store UNIX permissions, it may be used to compress other archive formats such as tar streams, and it is often used to pack stuffs like VM appliances or other huge files. In Mac Os X, you can handle .7z archives with the 7za utility, provided by the p7zip package, a 7-Zip implementation, available via MacPorts.

port install p7zip
# ...
7za [ l | x | a | .. ] 7zarchive.7z

To be told, if you plan to use this format for backups, consider that it lacks of recovery records, that means even if just limited file corruption occur, data may be lost.