Ability to RSVP for a category, so for our band we have percussion, trumpet, sax, etc.

We had a paid account, so we could add custom questions for the 100-person registration. Also, we liked that registrants could alter their registrations without our input.

The options that it provides is amazing. The set-up is easy. It's free! You can customize the fields to collect just about any data you can think of. You have the option of adding your own image or using one of their's. I have used this service many times over the years for various things - both personal and work-related.