Here are the upcoming events in the the Webinar in Additive Combinatorics (WAC), hosted by Sean Prendiville, Sarah Peluse, and myself. To gain admission to the live seminar you must register. Past talks can be viewed on youtube.
Here are some calendars of other online seminars in combinatorics, group theory, or other things in my sphere of research interest. Several subcalendars are imported from other places. One custom calendar is manually curated (a calendar of all events not in their own calendar, a variant of Russell’s paradox).
See also mathseminars.org.