Free to keep for a limited time!. https://store.steampowered.com/app/1294660/Divine_Knockout_DKO/ (Offer ends Wednesday at 10am Pacific Time.)

Free to keep for a limited time. https://store.steampowered.com/app/552500/Warhammer_Vermintide_2/

Mafia "classic" is free to keep for a limited time. https://store.steampowered.com/app/40990/Mafia/

Free to keep for a limited time. https://store.steampowered.com/app/699920/Despotism_3k/

"STAR WARS™: The Old Republic™" is apparently free to keep (the store page say free to play, but it should stay in your account even if uninstalled like a bought game would). https://store.steampowered.com/app/1286830/STAR_WARS_The_Old_Republic/