PayPal announced the winners of the PayPal X Developer Challenge, a competition to encourage the creation of innovative businesses using the PayPal X global payments platform. Rentalic, a person-to-person rental marketplace, took the top prize of $100,000 ($50,000 in cash and $50,000 in waived processing fees). Appbackr, a wholesale marketplace for iPhone applications, won $50,000 ($25,000 cash and $25,000 in waived processing fees).

Rentalic is an online person-to-person marketplace for owners to rent anything that they own, from vacation properties to camping equipment. Rentalic uses PayPal's preapproval API to validate that a customer has sufficient funds for a rental fee and deposit in a PayPal account before making a reservation. After the borrower returns the item or property back to the owner, the owner can provide feedback on the Rentalic site and fully or partially refund the deposit with the click of a button. Rentalic automatically takes a percentage of each rental.

Appbackr is the first wholesale digital marketplace for iPhone applications. Founder and CEO Trevor Cornwell said, "PayPal X is like a fiber optic network for moving micro-payments - simple, seamless and efficient. Making multi-party micropayments a reality is a complete game changer that creates new businesses that simply weren't possible before."

The two winners were among 650 submissions received.