Osk 4.71 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The software lies within Education Tools, more precisely Science. This Mac app is a product of Studlar Software.
From the developer:
With Osk, you can easily connect persons to one another, trace families, draw descendant trees, ancestor trees, and you can go back and forth with 10 generations, both ways. Difficult information like same sex marriages and adoptions are easily handled.
You may want to check out more Mac applications, such as Gee, Arcade Math Blocks or NLVM, which might be similar to Osk.