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1.
A combination of Digital Download Service--Steam, and Social Network--Facebook. Using a method of "fake shortcuts" via activating a "non-steam game", you can rename shortcuts to anything you want, simultaneously to Facebook's "status"; upon launching this "game", it'll alerts your entire friend list. Fully abusive. Blogs replaced with groups and their "announcements".

To distinct people that are using Steam as Steambook is quite easy: Their "steam rating" equivalent to be 0-1, whilst normal users has rating of 8-10. However, some individuals delude themselves and "pretending" to play game via "steam in-game layout" while game just running on a background; increasing your rating. Thus, for people to not condemn them in Steambooking.
Steam conversation example:

17:42 - Steam user: Wanna play tf2?
17:42 - Steambook user: Sure, give me a sec
Steam user is now playing Team Fortress 2. Click here to join.
17:55 - Steam user: Are you coming?
Steambook user is now Away.

18:00 - Steambook user: So where we left? Sorry, just some normal steam user wanted to play with me; got on my nerve. I'll be "away" for now.
18:02 - Steambook user #2: So, how's life and family? Brother still bullying you?
by z.x.t. May 21, 2012