Holiday list (credits to @erwdavid for hol2ics tool, which I used to convert my .hol to .ics)

README.md

Holidays to calendar

Outlook

Download sti.hol to your desktop, double-click and select STI from the Add Holidays to Calendar pop-up menu.

MacOS

Download sti.ics to your desktop, double-click to add it to calendar.

iOS

Email sti.ics file to yourself. Open the email on your iPhone or iPad and tap on the sti.ics file. In the following menu, click Add All to add all holidays to Calendar.

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Credits: Erwin David's hol2ics tool was used to convert sti.hol to sti.ics with the command:

ruby hol2ics.rb sti.hol

sti.hol

[STI 2018] 12
Makar Sankranti (Pongal), 2018/01/15
Republic Day, 2018/01/26
Good Friday, 2018/03/30
May Day, 2018/05/01
Independence Day, 2018/08/15
Id-ul Zuha (Bakr-Id), 2018/08/22
Ganesh Chaturthi, 2018/09/13
Gandhi Jayanti, 2018/10/02
Vijay Dashami (Dussehra), 2018/10/19
Kannada Rajyotsava Day, 2018/11/01
Deepavali, 2018/11/07
Christmas Day, 2018/12/25

sti.ics

BEGIN:VCALENDAR
PRODID:-//Hol2Ics//EN
BEGIN:VEVENT
SUMMARY:STI 2018: Makar Sankranti (Pongal)
DTSTART;VALUE=DATE:20180115
DTEND;VALUE=DATE:20180116
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Republic Day
DTSTART;VALUE=DATE:20180126
DTEND;VALUE=DATE:20180127
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Good Friday
DTSTART;VALUE=DATE:20180330
DTEND;VALUE=DATE:20180331
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: May Day
DTSTART;VALUE=DATE:20180501
DTEND;VALUE=DATE:20180502
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Independence Day
DTSTART;VALUE=DATE:20180815
DTEND;VALUE=DATE:20180816
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Id-ul Zuha (Bakr-Id)
DTSTART;VALUE=DATE:20180822
DTEND;VALUE=DATE:20180823
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Ganesh Chaturthi
DTSTART;VALUE=DATE:20180913
DTEND;VALUE=DATE:20180914
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Gandhi Jayanti
DTSTART;VALUE=DATE:20181002
DTEND;VALUE=DATE:20181003
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Vijay Dashami (Dussehra)
DTSTART;VALUE=DATE:20181019
DTEND;VALUE=DATE:20181020
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Kannada Rajyotsava Day
DTSTART;VALUE=DATE:20181101
DTEND;VALUE=DATE:20181102
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Deepavali
DTSTART;VALUE=DATE:20181107
DTEND;VALUE=DATE:20181108
END:VEVENT
BEGIN:VEVENT
SUMMARY:STI 2018: Christmas Day
DTSTART;VALUE=DATE:20181225
DTEND;VALUE=DATE:20181226
END:VEVENT
END:VCALENDAR