There’s a lot of different exercises a person can do to stay in shape, and have natural muscle without going to a gym, you think about it in a way is more convenient sometimes to do an exercise at your own time, because once you get in the habit you’ll keep doing it, instead of just been a one time thing that you do, and you stop.
Basic exercise push ups if you want to develop nice pec muscles, and some triceps you can do pushups, there’s different form of pushups you can do, there’s the regular pushups, or close grip pushups, you put your fingers together like a triangle, and you will do a regular pushups, except it’ll exert more force, and it’ll work your inner pec some more, and it’ll give you more strength.
You can do standing calf raises, you stand in front of a wall, put both hands in front of you against the wall, and lift up on your tip toes, this will work your inner, and outer calf muscle. You can do Reverse crunch scissor works out lower abs, upper all in one range of motion.
Get a treadmill, and run a couple of times a mile or two a day in your treadmill, and with time you’ll see results.
You can do bicycle crunches workouts upper, lower abs, oblique’s, you can do squats but without weights you could do 50 a day.
Most important thing is varied your workout routine, don’t always do the same things, or don’t do the same exercises all in one day. Change day to day what you do, and leave a day or two to rest, the more you rest, the more you varied, and change your routine, the more results you’ll get in the faster amount of time.