Holy chao! We didn’t realize that Pact was closing down. What an endorsement! So welcome to Beeminder 
For a goal to track your gym visits, you’ll want to set up a Do More goal and add a 1 to it every time you go to the gym. You can do that manually each time you visit the gym (we’ve got iOS and Android apps, which make it real easy to just quickly add a datapoint when you get to the gym).
If you want to get it set up to track you more automatically (and more publicly), you can do what I do here:
https://www.beeminder.com/b/lift
I set up the manual Do More goal, but then I made an IFTTT recipe to add data to my goal for me automatically whenever I check in at my gym on Swarm. [Hmm. I’m not seeing a way to share / publish a personal recipe on IFTTT – used to be an option but I can’t find it now… so here’s a picture of the recipe.
We also have a RunKeeper integration that’ll track your workouts with RunKeeper automatically – to see how that works you can start here: Beeminder
Cheers!
Bethany