It was started before Swift become more or less mature, so the whole codebase is in Objective-C.

Sounds like no plans for Windows platform? (I'm a multiple platform user.)

Sorry, no, it will require complete re-write and the app also heavily relies on OS X accessibility.

But I remember using ManicTime on Windows, give it a try maybe.

ManicTime looks slick, feature filled and usable, but the visualization it chose is confusing. I look at all those little lines and it reminds me of the windows XP defragger.

It is wonderful.

YMMW but IMO it is a shining example of modern Windows UX done right. A couple of examples

* double clicking selects the block you clicked on until next previously tagged time

* the tagging dialog has wonderful autocomplete

* you can set up automatic tagging

* you can add timelines from outlook etc