What is a free alternative to winzip?

I recommend using 7-Zip. 7-Zip is an open source file archiver with high compression ratio.

7-Zip has a strong community backing and unlike WinZip and WinRAR is completely free (contrary to popular belief WinRAR and WinZip are not free though you can continue to use the trial periods if you don’t mind pop-up boxes).

7Zip – Free Compression/Archiving software (Alternative to winrar+ winzip)