Here's a calendar of events I maintain for my own reference: conferences, workshops, hackathons and gatherings related to Open Development and technology I am interested in.
You can add it to your own calendar application, and if you'd like to collaborate: I'd be happy to share more relevant events!
Disclaimer: I cannot guarantee all these events are correct and legitimate. I do some basic checks and provide a link to information, and would be grateful to receive corrections.
My events watch list
I've used different platforms to maintain lists of events in the past, most notably upcoming.org and Lanyrd. Our Open Development guide on Lanyrd worked for some time, but by mid-2016, a few years after the site was bought by Eventbrite, it became unreliable, and I've had occasions where I couldn't get the information out of it when I needed. By now, Lanyrd is gone, as happened to Upcoming before.
So I've moved everything into a Google Calendar, to serve my personal needs, and maybe have a bit more longevity.