Offer swap for alternate exercises for situations where equipment isn't available
For instance, if the fly machine is taken, give the client the ability to toggle an alternate which would display DB flys (or whatever I choose to offer)
Heather Turco Blackmon commented
You could also use this concept to offer home exercise options on a program that is written for a gym workout. So if barbell squat is the main exercise, you could show a dumbbell squat as the alternate. Would be good to allow the user to pin which exercise they want displays on future weeks the same workout is programmed.