There are no key differences between cappuccino makers and espresso machines because they both make concentrated coffee and steam milk. Espresso is an intense, 1 1/2-ounce extraction of coffee that doesn't include milk. Cappuccino includes equal parts espresso and frothed milk.
The two major types of espresso machines are steam driven and pump driven. Steam-driven machines use steam to force water through the coffee grounds. Pump-driven machines use an internal pump to force water through the coffee grounds, resulting in a brew that has more flavor. Steam-driven machines usually are less expensive than pump-driven machines, but the downside is that most produce a maximum of four espresso shots and they must cool down in between uses.