The gym I used to coach at offered Parent's Night Out (3ish hours of gym time and pizza) every Friday and Saturday evening during the school year and I think once a week during the summer. In addition to this they had open gym for teens/adults I think 2 or 3 evenings a week (it was in a college town, so these were usually a big hit). They would sometimes set up a slackline, obstacle courses, parkour type set-ups, or options for skiers/snowboarders during these times.
They offered open gym rentals for birthday parties, school groups, church groups, girl/boy scouts, pretty much anything you could imagine. They were pretty low-key events, though it could be arranged to have a party room available for those that wanted space for presents and cake.
They offered private or small group lessons, not only for current students, but also for girls looking to develop skills for dance or cheer. I think now they might be offering a class solely for acro for dancers as well as karate and an aerial silks class. They almost always have something going on and revamp and add classes periodically to spice things up and bring in new customers.