• Skip rope. Grows stamina, heart and other muscle strength, breathing strength, probably balance as well
• Commute/move around by walking/bicycling. Chain with the public transport if possible and if the distance is otherwise too big (I have cycled tens of thousands of kilometers just to get to school/work/leisure time places)
• Check out the multi-stage fitness test! Here's one video you can try out!
• Try out dancing! If it's fast enough, it can be one of the most effective fitness activities there is! Trains your body, trains your brain (familiarize and learn movement patterns and pace them with them music) and trains your social skills (if you do dances that require partner(s))

Some tricks:

• Gamification. Habitica as an example. Take/infuse your favorite game mechanics to your exercises! Come up with a nice reward system!
• Follow progress. Write down the reps, time periods done and other information to see that you have actually developed! You can play with making charts to visualize this even further!
• Distract yourself while at it. Watch a movie, listen at music/podcast
• Build some kind of a exercise plan. At the gym as an example. What you do, how often, how long breaks and how often, what muscles it affects. Alone or by the help of someone else
• Don't do it alone! Exercising with friends can be at least double the fun!
• Challenges! "I will do x amount of x, before x o'clock, x times in a day, x days in a week!" You can also challenge friends to do the same stuff and even come up with a chart or start using an app that follows everyone's exercise for some competing!
• Start with a too easy plan that you do less often. Rise up the reps and the cooldown in between with the slightest (It's not exercise but I started being less at the computer by 1min in day 1, 2min in day 2, 3min in day 3 etc. Now I'm at 166min/day)! This helps building a new habit. And don't be afraid if you fail to do stuff a couple of times - try again or lower the requirements. A little is always better than none at all!
• Find cheap equipment at recycling centers! I like tennis and found a racket or two in 20€ in an excellent shape (they can cost hundreds as new)!

Some gamification ideas:

• Collect resources through reps. You can build stuff with them - buildings and villages, machines, whatever!
• Collect followers through reps. Come up with a cause that can make it fun!
• Collect strength, wisdom, power through reps. Beat up more and more difficult opponents and reach godhood (or something else)!
• Advance in evolution with reps. Start as the smallest speckle of life, eat, grow, mutate and become the most epic creature there is!
• Advance a quest line or something else with reps. Become a squire and then a knight and later a king or save up the world little by little or whatever!
• Collect particles with reps. Build protons, neutrons, electrons with them and further build every atom there is in the existence!
• Build up a factory or something. Reps can be money.
• Draw a Tetris box on the paper. Come up with activities/reps and determine a shape for each. Then fill your Tetris box with those shapes by doing the required things! You can make different box sizes, shapes and build even level categories that include many different levels (like, Easy category which has smaller boxes, mediocre that has bigger ones etc)

Remember: Make it as fun as you can, and you'll create a habit more easily!