Open Source Folder Compression Utility -- 7 Zip
If you need a free tool to open zipped files, tar files, or other types of compressed folders, and to likewise zip folders yourself, check out 7 Zip. I've been using it for a month now (after my Power Archiver trial ended), and I've found 7 zip does everything I ever need it to -- and it's free.
Here's their site: http://www.7-zip.org
