This is a highly customizable spreadsheet calendar with defaults set for the Pathfinder RPG, though it can be used for any RPG. Specifically this is the Absalom Reckoning(AR) calendar.
On the main sheet you can change:
the year, automatically updates the days events, holidays
how often leap years occur, default 8. This one is specified in the Pathfinder canon but there's good reason to change it.
Moon cycles, how often and when they start
There is also an 'Events' sheet that allows changing or adding events and holidays to the calendar.
There is now a Blood Of The Moon version with moon names.
Exact dates of moon quarters may not coincide precisely with those listed in Blood Of The Moon. The algorithm is fairly simple, does not consider elliptical orbit etc.
Quarter moon phases can be tracked as events in the Events sheet by referencing a 'phase chart' in the CORE sheet.