Most of the sites are privately owned, although some are public or backed by larger travel companies. Some sites specialize in creating and selling their own offers. They post discounts the companies choose to offer and link buyers directly to sites where they can make purchases. Then there are the Web sites that sell all types of travel, including the last-minute variety. Not surprisingly, major restrictions are often imposed on last-minute bookings.
Travelers can also sign up for sites' electronic mailing lists.
Many sites send out regular e-mail alerts, some tailored to their customers' individual interests.