Ask How do you set up a waitlist system to for a membership site?

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I've seen some membership sites use a waitlist system, and it seems like a good idea. I'm not sure how to set one up or what the benefits are. Do I need special software, or can I just use email lists? Should I offer something to people who join the waitlist? I want to make sure it keeps people interested and ready to sign up when spots open. How do you set up an effective waitlist system for a membership site?