Hello,
If you are only going to use the RSVP-style tickets, then you do not technically need to have WooCommerce or Easy Digital Downloads…however, you will see a notice at the top of the screen in the admin area prompting you to activate WooCommerce/EDD, as it is technically a required plugin for Event Tickets Plus. Without it, you won’t see the option to add a new ticket (only an RSVP).
If you do activate it, you can still create free tickets by entering a price of $0. I would recommend taking a look at the following articles, which have lots of good info on getting up and running with Event Tickets Plus:
New User Primer: Event Tickets and Event Tickets Plus
Settings Overview: Event Tickets and Event Tickets Plus
Managing Your Orders and Attendees
Moving Tickets
Please let me know if you have any other questions!
Thanks,
Jennifer