Sometimes, when you run 2 different .ZIP programs on the same data (PKZIP & KZIP for example), some files get compressed better in one program, while other files get compressed better in the other.
 
The ZIPMIX application was designed to take the best files from each one and create a new output file, which is guaranteed to be equal to or smaller in size to both of the input files. ZIPMIX can also be used to perform boolean operations on ZIP files, such as merging 2 ZIP files together, or updating a new file (with some tricks).