What's your to-go app for physical exercise or workout?

I don't use an app, but I probably would if it could connect to the gym equipment I'm using. I've seen that Matrix has something like that: https://apps.apple.com/us/app/ma... Here's a business idea: Find an equipment maker that hasn't got an app yet, and provide them with one. There may be a gap in the market in that sense.

I only use my calendar - it reminds me when to go to the gym.