Illustrations I made for Mail.ru web calendar,  they show some of the unusual holidays of the year. Agency: Viuga Bureau

The Day of the Programmer is an international professional day that is celebrated on the 256th day of each year, September 13 or 12.

Pi Day is celebrated on March 14th (3/14) around the world. Pi (Greek letter “π”) is the symbol used in mathematics to represent a constant — the ratio of the circumference of a circle to its diameter — which is approximately 3.14159.

System Administrator Appreciation Day, also known as Sysadmin Day, SysAdminDay,  exists to show appreciation for the work of sysadmins and other IT workers. It is celebrated on the last Friday in July.

International Internet-Free Day suggest that you spend the last Sunday of January without using the Internet.

Russia's largest postal service Mail.ru celebrates birthday on October 15

World Webmasters Day is celebrated on  April 4