The reverse chair squat is a squat that enforces good squat technique because the chair back makes you want to straighten your back, and the "horse rider” stance means that your knees will correctly track forward over your midfoot.
If you don't put your hips back to the wall behind, your knees will collide with the chair. Once in the squat you can enjoy all sorts of arm positions and play with unequal feet.
Two minutes total. Enjoy!