There are many interesting traditions of exercise from around the world. I only refer to them as "alternative" from a western/American perspective, but of course what is "alternative" here may be very common and mainstream in another part of the world. Exercises such as yoga and tai-chi are very low-impact, and both not only are good for the body, but also the mind. They are contrasted with the more robust/high impact American styles of exercise which have developed over the last few decades, such as aerobics, jogging/running, power-walking and weight training. Which is better? It depends on your physical needs, your age and other factors. For most people, all of the above is good, because the different exercise systems help the body and mind in different ways. So there is nothing wrong with doing strenuous American-style exercise and then doing something like yoga or tai-chi, either directly afterward or later in the day or week.
More, on Wikipedia:
Tai Chi
Yoga
