Foam rollers are famous for giving great massages: you just roll your target body part over this handy cylinder. But you can also use a roller as part of a strength workout, where it fills in for exercises that might normally use an exercise ball or a yoga block.
For example, you can do a plank with your hands on the roller, as an added stability challenge to your core muscles. The roller can also help to position your arms in a squat (holding the roller above you) or in a warrior 3 type pose, holding it behind you.
Using a roller can make one-legged squats more attainable, or give hamstring bridges an extra challenge. Greatist gives some ideas for how to work all of these foam roller exercises into a workout, so check out all the moves at the link below.