OpenTable is a paid service that handles online reservations for restaurants. It consists of a customer-facing web site, to which restaurants link using a custom URL in order to provide their customers with the service, and a Windows application running on a PC at the client's location. This application apparently contains the reservation database.
In order for the service to work, no less than three incoming TCP ports (2368,6319, and 6320) must be routed to the target machine, making the service very prone to breakage if the network configuration is changed. It is not clear why this is necessary, but it suggests that the software may have been cobbled together using several different comm components with overlapping functions rather than being written as an integrated whole.