A beta version of Family Diagram is available now to the public!
While the beta diagram is fully functional is free of charge, the app will only be available on a paid subscription basis once it is released in the Mac App Store. A subscription will cost in the range of $150-$200/year and will support the significant cost of ongoing development. From that point on you will not be able to use the diagrams you create without buying a subscription to use the app.
However, anyone will be able to download and use the app for a single diagram. It is unclear at this point whether it will be possible to important an existing diagram into that one free diagram.
The beta currently only run-on macOS. The oldest version supported is High Sierra.