AddThis is a social bookmarking service that can be integrated into a website with the use of a web widget.
Alexa Certified Site Metrics is an analytics service wich monitors and analyses web traffic and can be used to keep track of user behavior.
Google AdSense is a program run by Google through which website publishers serve advertisements that are targeted to the site content and audience.
Nginx is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.