zip files

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I use StuffIt does what it says on the tin

 

There's a compression tool built into Mac OS X. Just select files, right-click and select "Compress x items". Or double-click a zip file to open. There are also 3rd party apps, such as StuffIt Expander or UnRarX or The Unarchiver or iZip

 

Do you want to extract them or create them?
Because both tools are already built into Mac OS X.
Double click on a .zip file to extract it, and select several files or folder and right-click and select Compress to make a .zip file.

 

This may be of some use:

Helpful Information for Any Mac User
Portables Fast Start: The New User's Guide to Apple Notebooks