[Free Sega DELISTED Retro-style Titles]
Streets of Kamurocho: steam://install/1368430
Armor of Heroes: steam://install/1368440
Endless Zone: steam://install/1368450
Golden Axed: steam://install/1368460
8-Bit Bayonetta: steam://install/567090

[Free Games]
Get WizardWizard. A fun, free platformer, accursedly infuriating. GREAT STUFF!:
http://www.indiedb.com/games/wizardwizard

Updated Free games list:
https://steamdb.info/sales/?min_discount=95&min_rating=0
or
https://web.archive.org/web/20170531213811/http://forums.steampowered.com:80/forums/showthread.php?t=851573

Rated list:
https://steam250.com/tag/free_to_play

Reddit posts:
https://www.reddit.com/r/Steam/comments/57fljf/the_list_of_really_free_steam_games/
https://www.reddit.com/r/Games/comments/1asysg/the_100_best_free_pc_games/

Upcoming free titles:
https://steamdb.info/upcoming/free/

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[Reusing Old Games]
Games from 3rd parties that can be registered on Steam: https://web.archive.org/web/20160505042257/https://support.steampowered.com/kb_article.php?ref=7480-WUSF-3601


[Other]
Mod for Starbound to turn it into a Mass Effect themed game: http://www.pcgamer.com/2014/02/02/mod-of-the-week-mass-effect-edition-for-starbound

Understanding Steam Trading Cards
http://steamproxy.com/sharedfiles/filedetails/?id=145245037