I often attend open source activities offline, but remembering the date and location of those activities is not easy. In China, I just collect those information from mailing list, WeChat or Telegram, then add them to Calendar.app on my iPhone manually.
There is a method to publish your activities on Internet, and it is called iCalendar, which is defined by RFC 2445. I can easily publish a public calendar using my iPhone via iCloud or via Google Calendar. Though it is not very GNU, but so far so good, at least it works.
Then I want to display it on my blog or website.
After a few google clicks, I found out that there is already an ugly service called 'zetabee'.
But still you have to rely on the service provided by zetabee, and it is far from simple and beautiful.
This project is one of its kind!