Hi Maxim,
Thanks so much for your interest in our plugins–glad to hear that you’re enjoying The Events Calendar so far! 🙂 It sounds like most of your requirements here should be met by our free ticketing plugin, Event Tickets, which includes support for RSVPs, allows event organizers to view RSVPs and check in attendees at events, and allows users to edit or remove their RSVPs after registering. Unfortunately, Event Tickets does not include built-in support for gotowebinar.com, though depending on the platform, you may be able to add some type of integration through custom development. I’d suggest reaching out to technical support for gotowebinar.com with any questions you might have about possible integrations!
I hope that helps to get you started here! Thanks again for your interest, and let us know if you should have any other questions!