The pistol squat is a great unilateral bodyweight exercise that improves balance and mobility!
Beginners can start with a box or bench.
Keep one leg up while sitting on a bench and stand up.
More advanced individuals can leverage the bench by standing on one side of the bench and balancing off of the side.
Once you've advanced beyond that, you can remove the bench and perform traditional pistol squats with one leg at a time going to depth.