When he was governor of Massachusetts, Mitt Romney introduced a type of health care for his state. It was one if his major achievements. Obamacare is based on the Massachusetts model, which is something the Republicans really don't want you to remember.
It is so hypocritical of them - they were all over Romney in Massachusetts, but they pretend it never happened now.
They're the exact same thing, except that Romneycare (Rc) doesn't mandate businesses to provide insurance. Romneycare was the model that Obamacare was built on, the "lab rat" if you will. The downside of Rc is that it only works in Mass. ie. if someone gets in an accident in another state, they're not covered under Rc. Here's a rundown by Forbes