Hi Erik,
We've been using EngagedPatrons (https://engagedpatrons.org/) for our registration. It's a bit clunky, but it does what we need it to most of the time. Specifically, it does allow you to limit registration and then automatically waitlists additional folks, which is super helpful. And, it's free to qualifying public libraries (those receiving less than $1 million dollars per year in total income). Larger libraries pay an annual fee; selected services are free to all.
Good luck!
Catherine
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Catherine Barnett
Programming & Outreach Supervisor
Chillicothe Public Library District
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