We are confident, as per Apple's June 2018 announcement of the MacOS Mojave version as their next OS, that FocusTune will run under Mojave. (And here in October 2018, we can confirm that Focustune 4.0.xx does run under Mojave).
And for beyond that....
We have decided to re-write our application for 64-bit mode. This should ensure that FocusTune will run under macOS and WIndows for the foreseeable future. The FocusTune 64-bit mode version is planned for release during the first half of 2019, and will be a paid upgrade.
Please feel free to ask any additional questions or concerns..