Talking about mods, I also presume that a lot of you know of Garrys Mod. Personally I'm shit at building stuff that looks decent though I still find it fun. Recently I've been getting back into it and a community I am a part of has launched a 12-slot build server. If you wish to visit it, the ip is: 220.127.116.11:27015.
Some of the other stuff I find can be quite entertaining on Gmod is Spacebuild, building stuff to go in space, and Rp, roleplay though I more just join friends in that and annoy them as a hobo.
Even though this isn't a review or anything, I'd say get Garrys Mod. Don't have the money? Get Gmod 9 but thats not supported so don't go complaining when everything breaks.