ZipCalc 3.1 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. ZipCalc for Mac lies within Business Tools, more precisely Vertical Market Apps. We recommend checking the downloaded files with any free antivirus.
From the developer:
ZipCalc measures distance between zipcodes and finds other zipcodes in a given radius. It also exports zipcode lists or SCF lists. It processes your mailing list, pulling out addresses that are not within a certain radius.
You may want to check out more Mac applications, such as NRGship for UPS, FakeNES or quickorder, which might be related to ZipCalc.