Jszip

What do you like best?

It's a tiny little script that does just this, and it's free. If you need to read (but not extract, obviously) ZIP files from your local PC via your browser, or create them from e.g. blob fields or canvas objects on the client side without a trip to the server, this is the script to use. It has good documentation, with easily understandable examples to get you going and warn you about common issues and misconceptions.

What do you dislike?

The script itself is very well made but the Javascript implementation in the browser have many little quirks when dealing with ZIP files (memory limits, differences between input and output archives, subfolders, encrypted or password protected ZIP files, the Mac Finder nitpicking etc.) , so if you are experiencing issues you know who it is to blame (and maybe in the docs you'll find a hint that helps you).

Recommendations to others considering the product:

If generating a ZIP file on the client side in a browser is what you need, and you don't want to mess with the Javascript API yourself, JSZip is as good as it gets — but beware of browser limitations!

What problems are you solving with the product? What benefits have you realized?

We used this in a project where we needed to allow the user to download something he had created in the web app, but hadn't PHP available to create a ZIP file server side, so we tried JSZip and were satisfied with the results.