7-Zip is open source software. Most of source code is under GNU LGPL license. AES code is under BSD LICENSE. unRAR code is under mixed license: 

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 compression ratio that is 2-10 % better than 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