Windows 2003, Windows Vista, Windows Me, Windows XP, Windows 2000, Windows NT, Windows 98
No additional requirements
Publisher's description 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: ARJ, CAB, CHM, CPIO, DEB, DMG, HFS, ISO, LZH, LZMA, MSI, NSIS, RAR, RPM, UDF, WIM, XAR and Z. 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.
It's easy for Windows users to forget that WinZip isn't the only file-compression utility in the world. Like its better-known competitors, the free 7-Zip unpacks a host of archive formats, including ZIP, TAR, GZ, and its own 7z format. Unlike WinZip, though, it can create TAR and GZ archives, which are commonly used on Unix and Linux systems.
The program's ability to shrink files was stunning. In our tests, 7z archives were up to 40 percent smaller then their ZIP equivalents, although compression did take longer, and the highest compression settings can hog system resources. Advanced options include the ability to create solid and self-extracting archives, and to adjust the compression level and password protection. The program also has a command line module. Though the main interface is overly simple and looks like it was designed for Windows 95, it's not hard to use and fairly self-explanatory. The context menu options, which include "testing" an archive, indicate that 7-Zip should be taken seriously.