http://www.steamgifts.com/ Free Steam games and Steam keys.
Users sign-in using their Steam account, and we require their account to be valued at $100 or greater. Games that have been accessible through bundles, or games that were once available for free due to promotions or pricing errors are not included in this calculation. We have this requirement in place to prevent users from registering multiple accounts. http://www.steamgifts.com/about/faq
http://www.sgtools.info/
Easily check your detailed contributor value and if your giveaway winners are following the rules!

https://steamcompanion.com/gifts/
SteamCompanion is a website that provides custom apps and services for Steam users.Check the latest market statistics, win free gifts, calculate your account's worth and more!
https://steamcompanion.com/faq

https://www.reddit.com/r/FreeGameFindings/
This sub is based around finding free games all over the place! Be it Steam, Origin, Uplay, Xbox 360/One, Playstation 3/4/Vita, or Wii U/3DS

https://steamcommunity.com/id/swappy
Swappy is a bot, designed to help you complete your card sets.