Support event recurrence relative to date completed
Moo.do ALMOST works as a replacement for Todoist (https://todoist.com/). The one feature it's missing is also Todoist's killer feature: The ability to have a task reoccur X days after COMPLETION, in addition to X days after its due date.
In the Todoist case, specifying that a task reoccurs "every 3 days starting Aug 1" will mean that the task will initially be due on 8/1, then 8/4, then 8/7, etc. Alternately, and more powerfully, specifying that a task reoccurs "every! 3 days starting Aug 1" (note the "!") will mean that the task will initially be due on 8/1, but if I don't complete it until 8/3 then the next recurrence will be scheduled for 8/6 (rather than 8/4).
(See the last "quick tip" box here: https://support.todoist.com/hc/en-us/articles/205325931-Due-Dates-Times)
Both types of recurrence have a role. For example, I'd want to use the type of recurrence that Moo.do currently supports when the date is more important, like scheduling a bill ("pay rent every month starting Aug 20"), while for something like watering my plants where the TIME BETWEEN tasks is more important I'd want to use the alternate formulation ("water plants every! week starting Aug 1").