Kayak. Kayak-App.jpg. Available in over 30 countries and 18 languages, that lets you search multiple travel sites at once from online travel agencies to airlines. Feb 4, 2013. KAYAK — an exceptionally useful travel price comparison site. and direct queries of dozens of online travel agencies, airlines, and discount. the over one billion annual queries performed on KAYAK sites and mobile apps. Sites and apps that compare. through third-party travel…