Amazon S3 or Amazon Simple Storage Service is a service offered by Amazon Web Services (AWS) that provides object storage through a web service interface.
Facebook pixel is an analytics tool that allows you to measure the effectiveness of your advertising.
HTTP Strict Transport Security (HSTS) informs browsers that the site should only be accessed using HTTPS.
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.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.