The Smith machine squat will allow you to safely squat a heavy weight in the absence of a spotter. Just make sure that you use the safety pins.
The trap bar farmer's walk is a great whole-body exercise for improving functional fitness, enhancing unilateral leg strength, and boosting overall strength.
The trap bar deadlift is great for building glutes, legs, back and forearms; strengthening the core; improving functional fitness; and developing strength.
Activating your knee flexors, especially your hamstrings, the assisted inverse leg curl with lat pull-down machine can be dangerous.
Use the dumbbell box squat to eliminate the stretch reflex, making the exercise more difficult and allowing you to overload your muscles with less weight.
If you don't have access to a leg curl machine, try the inverse leg curl on lat pull-down machine, an isolated pull exercise that targets your hamstrings.
Use the barbell front box squat to strengthen your front squat strength. It's also useful if you have knee problems, as it requires less weight.
The inverse leg curl (aka bodyweight or Nordic hamstring curl) is useful for working your hamstrings in the absence of a leg-curling machine.
Use the stability ball leg curl to work your hamstrings in the absence of a leg-curling machine. To make it more difficult, perform it with one leg.
The lying single straight-leg hip extension is not an effective exercise for overloading your hamstrings. Use it only when you do not have access to a gym.
The Smith machine bent-knee good morning, an isolation exercise, targets your gluteus maximus. Movement in the knees should be kept to a minimum.
Targeting your erector spinae, use the flat bench hyperextension only if you do not have access to a hyperextension bench. The range of motion is limited.