Hi Blair!
Thanks for reaching out to us!
Our Event Tickets plus plugin offers this type of functionality. Users can purchase a ticket and admins can access attendee information on the backend and export the information to CSV as needed. When your event begins, you or your staff can mark guests as checked in manually or by scanning the QR code on their ticket.
They were also wondering if users who have not already RSVPd to the event could check in and enter their information at the door.
I’m not really sure what you mean by this, but logged in users that purchased tickets can then access their account and edit their attendee information.
As a reference, you can check the following article that walks you through how to create tickets for your events > https://theeventscalendar.com/knowledgebase/making-tickets/
I hope that helps. Let me know if you have any follow up questions 🙂
Best,
Victor