Amazon's Mechanical Turk platform is different from the other freelancing sites for multiple reasons.
For one, it's owned by one of the largest companies in existence (Amazon). It also does not use the adversarial system of competing with other freelancers for assignments. Further, freelancers have the option of being paid with cash or with Amazon store credit, which is a lot like cash, but can be used on Amazon.com. There is no penalty for taking cash versus store credit.
The assignments vary by employer and range in pay from $0.01 to $10.00. Obtaining the high dollar assignments is hard as they are few and far between, but the lower priced ones are numerous.
The assignments on this site are way different than what you will find on other freelancing sites, and that's not just hyperbole.
The vast majority of the assignments on this site are menial tasks. Extremely menial. Like, looking at a shopping receipt and listing the items that were purchased, how much each item was, what store they were bought at, how many bottles of washing detergent did the person buy, what brand, etc.
There are many surveys that pay $0.25 to $0.50 sponsored by several university's Psychology departments.
Each assignment on Mechanical Turk takes anywhere from one minute to twenty minutes to complete, so a freelancer can make a few dollars while waiting for emails from other clients to come in.
Its website is www.mturk.com.