Audio Books Corner is an online audiobook store that is available worldwide. It also offers some free downloads. There is no monthly subscription. No extra softwares needed for playing their audiobooks.
Paperback Swap is an online bookstore that is a little different because it lets you swap books with other users on the site. If you have a book to offer, you list it on your profile. For each book you send, you get one credit. You can use that credit to request a book from someone else, or to get a discount for the books this store offers.
For registering on this site, you get two credits, which means two books free of charge.