With 46 million active users and over 300 Employees, Facebook could easily be called the new star of Social Networking. Facebook defines active users as people that have returned to the site within 30 days.

According to Facebook, it is the second most-trafficked PHP site in the world, and one of the largest MySQL installations anywhere, running thousands of databases. Facebook has built its own multi-language RPC (remote procedure call) framework that allows the company to seamlessly and easily tie together subsystems written in any language, running on any platform.

The company also claims to be the largest user of memcached, an open-source caching system, although it is not listed as such on Memcahed's list of users. It has created its own custom-built search engine which serves millions of queries a day, completely distributed and entirely in-memory, with real-time updates.

So, the question is, what are these 46 million active users spending their time on?

Current Top Ten Facebook applications:

1/ Top Friends
By Slide
What does it do? This application add a box of up to 32 of a users 'BFF's' (Best Friends Forever) to their profile, so they are one click away, and the user does not have to search for them.
About the developer:Slide creates widgets including slide shows, guestbooks, skinFlix and FunPix - for social networking sites and blog platforms. It was launched in 2005, headquartered in San Francisco and founded by Max Levchin, co-founder of PayPAl. It is backed by Mayfield Fund, Blue Run Ventures, Khosla Ventures and Founders Fun.
Amount of daily active users: 3,073,371

2/ FunWall
By Daniel C. Silverstein and Bobby Joe
What does it do? FunWall is a "next level app" that lets users add text, custom pictures and YouTube videos to their own wall and friends' walls.
Amount of daily active users: 2,374,629

3/Super Wall
By Jia Shen
What does it do? Super Wall also lets users write messages, post photos, and videos on their wall
Amount of daily active users: 1,382,494

4/SuperPoke!
By Nikil Gandhy, Jonathan Hsu and Will Liu
What does it do? It enables users to "do" any one of a number of "actions" to any of their friends that also have the application installed. Actions included pinching, hugging, tickling, and throwing sheep. Users can customize what options show up on their page
Amount of daily active users: 1,246,654

5/ Video
By Facebook
What does it do? Facebook Video enables users to publish personal video and tag friends on Facebook by uploading files, sending video from mobile phones, or recording directly from webcams. It also enables users to send video messages to friends.
Amount of daily active users: 994,137