Tempeh belongs the the same family as tofu, seitan, and other soy products. Unlike tofu, tempeh is actually made from fermented soy. The fact that tempeh is fermented should not be overlooked, because it actually makes the protein more easily digested. The fermentation process also increases the bioavailability and solubility of nutrients such as calcium. Tempeh is also less processed as compared to tofu, and you can see the partially compressed soybeans that make up the tempeh patty. It’s texture is “meaty,” its flavor has a subtle nuttiness, and it takes on flavors well (so you can use it in many different dishes!). Tempeh is impressively high in protein- 1 cup contains 31 grams, as compared to 10 grams in 1 cup of tofu! It also contains high levels of calcium (18% of daily value for 1 cup), iron (25%), vitamin B-6 (20%), and magnesium (33%).
You can find tempeh in the refrigerated section of the grocery store where the other soy products are located.
(Sources: http://www.popsugar.com/fitness/Difference-Between-Tofu-Tempeh-1034188, USDA.org, http://www.caloriecount.com/calories-tempeh-i16114, http://www.whfoods.com/genpage.php/genpage.php?tname=foodspice&dbid=126)