Hey Hannah,
Thanks for reaching out – we unfortunately don’t have this feature with our ticketing plugins at the moment, and even “Free” tickets would, at this time, require going through a checkout process (i.e. “purchasing” the free tickets).
However, in our upcoming version of The Events Calendar, version 4.0, we have some simple RSVP features that pretty achieve what you described here:
It’s just to get an idea of attendee names and numbers, really.
I don’t have a definitive release date for the 4.0 update, but it should be here by Thanksgiving Day if all goes to plan.
Let me know what you think about this and if I can help anything else!
Sincerely,
George