Certain forms of yoga (Astanga is the "power yoga") & pilates can be used for toning, flexibility, balance, concentration, coordination & weight loss... but you'll only build bone density by weight-training. Also, there are no studies (that I know of, someone tell me if you know of one) that proves yoga or pilates can build as much muscle as weight training.
That being said, I agree with Stef that you have to find a balance of exercise that you enjoy doing (or at least you don't
despise it, lol) - or you won't stick with it in the long run & you won't get as much out of it while you're doing it.