I agree with PPs who are giving the advice that crowd calendars aren't very useful anymore.
There's essentially three crowd levels:
1. Insane - These are Christmas, Columbus day weekend, Easter
2. Very Busy - Spring break month, Other long holidays like Memorial day, Weekends at MK/Epcot with F&W
3. Busy - Every other day
The problem with searching for the unicorn that would be "low crowds" is that WDW staffs according to crowds. So even if you find a day with low crowds, its probably going to be staffed accordingly, making your waits about the same as if it were at least #3 above.
Heavy rains clear out the crowds, so if you don't mind rain, as a PP stated, check out the weather (which is also a futile attempt in FL).
Good luck!