Zip files without compression

The ZIP format has always supported archiving files with zero compression ratio, even since pkzip/pkunzip in DOS times.

Nowadays, almost all compression programs support this; 7-Zip is one of them, it lets you specify the compression ratio both from the GUI and from the command line, and it's free.

For Linux this shell command zips mydir folder with no compression:

zip -0 -r mydir.zip mydir

Info-ZIP's zip, which is open source, free, and already installed on most Unixish systems has a "-0" option to store only.

Also if you simply zip with any zipper and the entries would be shorter stored than compressed, which is what happens with already compressed files, then they will be stored automagically. However if you already know they're compressed, then it's faster to just tell zip to that with -0.