7-Zip Copyright (C) 1999-2018 Igor Pavlov.
7-Zip is free software with open source.
The most of the code is under the GNU LGPL license. Some parts of the code are under the BSD 3-clause License. Also there is unRAR license restriction for some parts of the code.
Read file License.txt for full information about license.
Note: 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.