7-Zip 9.20 source code from 7-zip.org http://www.7-zip.org/download.html
License
7-Zip 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: license.txt
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.