AddThis is a social bookmarking service that can be integrated into a website with the use of a web widget.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
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.
PHP is a general-purpose scripting language used for web development.
Prototype is a JavaScript Framework that aims to ease development of web applications.