7-Zip is open source software. Most of the source code is under the GNU LGPL license. The AES code is under a BSD 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. But you can make a donation to support further development of 7-Zip.

The main features of 7-Zip
High compression ratio in new 7z format with LZMA compression
Supported formats:
Packing / unpacking: 7z, ZIP, GZIP, BZIP2 and TAR
Unpacking only: RAR, CAB, ISO, ARJ, LZH, CHM, Z, CPIO, RPM, DEB and NSIS
For ZIP and GZIP formats, 7-Zip provides a compression ratio that is 2-10 % better than the ratio provided by PKZip and WinZip
Self-extracting capability for 7z format
Integration with Windows Shell
Powerful File Manager
Powerful command line version
Plugin for FAR Manager
Localizations for 63 languages