Display, create and modify Google calendar events
Data on national, regional, and religious holidays via API
Worldwide Holidays and Working Days
Catholic liturgical calendar
Lookup for a name and returns nameday date
Convert between Gregorian and Hebrew, fetch Shabbat and Holiday times, etc
Historical data regarding holidays
Protestant liturgical calendar
A (satirical) Evangelical liturgical calendar
Public holidays for more than 90 countries
Provides namedays for multiple countries
Database of ICS files for non working days
Simple REST API for checking working, non-working or short days for Russia, CIS, USA and other
Check if a date is a Russian holiday or not
Bank holidays in England and Wales, Scotland and Northern Ireland
A REST API to convert UnixTime to DateTime and DateTime to UnixTime