We have found a number of use cases where an association would want to set-up a "Free" member type. Oftentimes, the association will also want to renew those free memberships indefinitely. In Novi AMS, this is pretty simple to do.
If you don't want to charge members of a certain type, then don't add any dues rules. When Novi calculates the renewal, the system will know that your intent was to give a free membership.
Don't forget to set your renewal date and auto-renewal.