Hard money lenders tend to be private individuals (or small groups). Most of the hard money lenders I have talked to lend for the short term only, almost always for less than a year and usually only for 1-3 months.
Pros: As was mentioned, a hard money lender does not generally look at your credit score. You might be able to borrow 100% of your purchase price.
Cons: You pay a ton in interest. For example, recently a hard money lender approached some investors we work with. They wanted a 10% return, due at the end of three months. They quite often want the loan secured by real assets, your car or house or whatever.
If you know you can buy a property and turn it quickly at huge profit, and you can't get a standard mortgage, it might be one way to go. Some investors use hard money to get into the property, do some quick fixes to raise the property value, then get a new loan (based on the property's new, improved value) from a bank to pay off the hard money lender.