https://www.humblebundle.com/store/surviving-mars-deluxe-edition-free-game - Free for the next 3 days or until supplies last.
https://store.steampowered.com/sub/586694/?curator_clanid=4777282&utm_source=SteamDB - Free until the end of June.
https://store.steampowered.com/sub/589381/?curator_clanid=4777282&utm_source=SteamDB - Free until June 21st. (VR ONLY GAME)

You're welcome.