As indicated, there is already a post on this. This is an organization that expects some money to change hands, so I am therefore duplicating that other thread:
In the interests of full disclosure: This is an organization that charges money. Whether PDFs are useful to you will have to be your decision.
"Our goal is to provide Free public access for a month to 2 Million eBooks. During the rest of the year you may continue to download your selection of about 500,000 PDF eBooks by joining the World Public Library. Annual membership is only $8.95 per year."