As far as I can determine, there is no extant calendar that functions correctly for keeping track of non-date-specific periodicity of events.
What I mean is that, as is normal with working out, I want to have something that reoccurs for three days and then skips one day (rest day). Furthermore, if for some reason we miss a workout day I want to be able to move all the future events forward (into the future) for one day without changing the record of past events and of course while altering all future events without caring about specific dates but moving them all forward in time by one day.
This simply does not exist, as far as I can tell, even though it’d seem to be something commonly needed in the world of fitness. I find it hard to believe, but I’ve spent a few days searching and can’t find anything.