7-Zip is a reliable substitute for commercial products such as WinRAR and WinZip that offers a high compression ratio and, best of all, is completely free.
Supports a wide range of archives, besides default .7z format, is working with ZIP, RAR and others.
Can encrypt archives with password, includes a command line option, interface available in many languages, users can create or open archives through right click menu.
The default 7z extension offers a higher compression rate (file size is smaller) than other archive types made with this program or with other ones.