Although most hammers are simple hand-tools, there also exist mechanical hammers. Jackhammer, steam-powered hammer, hammer drill, high frequency impact treatment, trip hammer are some mechanically-powered hammers. These are used for heavy industrial jobs, but essentially work on the same principle of a hand-powered hammer.
Here's a list of 10 widely used hammers along with a picture of each. Also, read about the purpose for which each one is used.