7-Zip is one of strongest free archiving program out there. In addition to this, is also open source, which has spawned a number of free archiving tools based on the 7-Zip engine. A good thing, too, as under the hood this software packs quite a punch.
I recently downloaded a 4GB DVD ISO saved under RAR format and split into multiple archives. I was using IZarc as my archiving software and was surprised when the extracting process failed. I assumed it was a bad archive and was going to delete the files and move on when on a whim I decided to install try 7-Zip. Sure enough, the extraction worked. Great, I thought, a makeshift test that I could use to test different free archivers (ZipGenius, Quickzip, IZarc, and Extractnow failed to extract the file, while TUGzip and 7-Zip weresuccessful).
7-Zip will compress and extract archives in 7z, ZIP, GZIP, BZIP2 and TAR formats and will extract RAR, CAB, ISO, ARJ, LZH, CHM, Z, CPIO, RPM, DEB and NSIS formats. Although I dont use it (and am not planning to), the 7z (7zip) format is supposed to offer a higher compression ratio than either ZIP or RAR.
Cool things about 7-Zip: very simple interface, fast and powerful archiver, 2-10% better compression ratio for ZIP format (compared to Winzip and PKzip), many formats supported.
Not so cool: creates autoextract archives only for 7z format, no support for ACE format, could use more elegance/form factor, archive icon not very attractive (sounds silly but actually matters to me).
A free alternative to: Winzip, Winrar, PKzip, etc…
Version tested: 4.42