Downloading GeoKalk 6.6 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This free Mac app was originally designed by Nestor Cardozo. The software lies within Productivity Tools, more precisely Office Tools.
From the developer:
GeoKalk is a calculator for vectors (lines and planes) and tensors (strain and stress). Multiple calculators can be opened, edited, and saved. The entries and the results are presented in tables, as well as in a stereonet and a Mohr circle. In 3D stress, the stereonet and the Mohr circle can be colored by slip tendency. The entries can be read from text files. The results can be exported as text and plots.
You may want to check out more software for Mac, such as 3dissue, Blurb Tally or Pads X, which might be related to GeoKalk.