7-Zip is an open-source file archiver, that offers the highest compression ratio, using the new 7z format, which delivers compression results that are usually 30-50% better than standard ZIP.We tested it with a server log file, which compressed with ZIP had a file size of 18 mb and using 7-Zip was reduced to 8 Mb (results may vary, depending on file type).7Zip supports 7z,ZIP,CAB, RAR,ARJ,GZIP,BZIP2,TAR,CPIO,RPM and DEB formats, so it can be used with all popular archive files. The program offers a basic file explorer interface and also integrates into the Windows right-click menu. It can be associated with any of the supported formats and also offers command/line support.

Changes in 7-Zip 9.20 Final (2010-11-18):
- 7-Zip File Manager now can calculate SHA-256 checksum.
- Some bugs were fixed.

Changes in 7-Zip 9.20.07 Alpha(2011-03-14):
- 7-Zip now supports extended timestamp range in TAR archives (dates before 1970).
- There are some changes in code that creates temp files and temp folders.