HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
Kevel (formerly Adzerk) is a developer of ad-serving APIs to help developers build server-side ad platforms.
Open Graph is a protocol that is used to integrate any web page into the social graph.
PayPal is an online payments system that supports online money transfers and serves as an electronic alternative to traditional paper methods like checks and money orders.