You… probably don't need this to be explained to you, I figure
You can see a list of SB Steam people in the Hookup section.
A browser plug-in that adds a lot of nice features to the Steam website. For example it will tell you a game's lowest ever price, and it's current lowest price.
Firefox version has been discontinued due to Mozilla's new add-ons policy/requirements, but a pretty-much identical plug-in called Super Steam is now availible.
Ice is a tool that, with a little configuration via text files, will add all your ROMs to your Steam library, and launch them with whatever emulator you wish. The auto banner downloading element seems to be borked at the moment though.
Idle Master is a tool you can use to trick Steam into thinking games are running, so that you can get card sfor all your games before you actually install and play them. It requires you to sign-in throug Steam, and quietly runs in the background.
Steam is a bit of a memory hog. You can mitigate this somewhat by using the 'Metro for Steam' skin, which also makes it looks a bit more contemporary (ie: like Windows 8/10).