If you're looking for a tool to design and send out custom event cards, as well as track RSVPs, you might want to check out Coteri. This event planning tool lets you create custom event cards, manage contributions from guests, and track RSVPs by email, link or QR code. It also integrates with Canva if you want to use its templates. Other features include "what to bring" lists and machine learning-generated playlists based on the songs you select. With detailed RSVP tracking and support, Coteri is a good option for many types of events.
Another possibility is Softr, a no-code tool that lets you create custom client portals, internal tools and community hubs. Although its main purpose is to create custom portals, Softr's drag-and-drop interface and integration with tools like Zapier and Google Analytics could be used to create event-specific pages and track RSVPs. It takes a bit more technical work, but Softr offers flexibility and customization that could help with your event planning.