Calf raises, bodyweight, 1 foot at a time, 3x20/side
Hanging leg raises, feet to the bar, 3x6
... and Saturday went like this:
Body rows, under Smith bar, with biceps grip, 10x10-16
Triceps pushups, with elevated feet, 5x30
Diamond pushups, 5x12
Sunday was a rest day. I planned to do some back and shoulder training, but when I listened to my body it made it clear to me that I should stay away from the gym that day. I was content with some low intensity cardio, in the form of walking.
I really enjoyed the two workout sessions described above. They made me want to undergo a period where I put extra emphasis on bodyweight work at the gym.
Calisthenics are a great way to mix things up. Sometimes I see people online debating whether you can build muscle mass with bodyweight exercises only. The answer is yes, you absolutely can.