A thing about steam.

[black hawk]

Well it's been some time, since I last logged in. Internet is a problem in my area. Nevertheless, my problem is that I don't know much about steam except it is a place/website where I could buy games at a good discount or I could play some free games. What I wanted to know is whether it supports LAN gaming or you know something like Tunngle supports. Does it host some servers for online games (except those free ones)? If yes, then for which games.(older games between 2005 to 2009 would be more preferred.)