I skate (well, coach) year-round, so I keep cool all summer but I increase my activity as time is more available in the hotter months. To stay active, I use my fitness club membership or take a course like dance, Fitness Pump, fencing.
This year, I felt like I was in a rut, so I joined My Peak Fitness. (It's less expensive than WW and half the money goes to blood cancer charity, so it's okay.) All online with printable pdfs for reference and a private Facebook group for support. You can work out at a gym or DIY at home, no worries.
I like it so far! It has structure with flexibility and independence. There are workouts and (optional) menus for each day and it goes in Challenge cycles, so I don't have to think about what to do and eat as much. I like the Challenge cycles and the laddering drills they use. I copy-and-paste the workouts into my Dropbox list tool, so I'm not killing trees and I can access the info at home or the gym.
What's everyone else doing for the summer?