From Thomas Tempelmann:
If you program in REALbasic, these classes allow you to create and read .zip files. ZIP files are the most popular compression archive format on DOS/Windows systems. Compatible with programs such as: WinZip, PKZip, ZipIt, Aladdin Expander and Stuffit DropZip. Another nice feature is that one can create and read "snapshot" archives, for incremental backups of the same set of files and folders.