7-Zip

This program is called "7-Zip". It is open source software. Most of the source code is under the GNU LGPL license. The unRAR code is under a mixed license: GNU LGPL + unRAR restrictions. Check license information here: 7-Zip license. You can use 7-Zip on any computer, including a computer in a commercial organization. You don't need to register or pay for 7-Zip. 

Windows
32 Bit
7z1700.exe - 1.1 MB

64 Bit
7z1700-x64.exe - 1.3 MB

Linux
p7zip_16.02_src_all.tar.bz2 - 4.0 MB