I invite you to look at mathseminars.org.
Anyone can create listings for seminars or conferences, either as an organizer or as a curator. These listings will automatically appear once the individual has been endorsed (similar to arXiv endorsing). The goal is to distribute the task of maintaining up to date listings as broadly as possible. When browsing talks and seminars, you can filter by topic or institution, tag your favorite talks or seminars, and export to your calendar (new talks in a seminar you have subscribed to will automatically show up in your calendar). Times are automatically translated to a user's local time zone.
We've added a few seminars that we found online. We are in the process of adding more. If you would like to join our efforts, you're very welcome!