https://store.steampowered.com/app/1597920/KARDS__Anniversary_Edition/
You need from the base game to get this.
“Free to keep when you get it before 19 Apr @ 2:00pm.”
https://store.steampowered.com/app/544810/KARDS__The_WWII_Card_Game/
https://store.steampowered.com/app/988730/Heavy_Metal_Machines__Dirt_Devil_Pack/
You need from base game to claim it.
https://store.steampowered.com/app/331360/Heavy_Metal_Machines/
https://na.alienwarearena.com/ucf/show/2152248
You need from base game to claim it. Keys won’t last long so get one ASAP.
The official website also has a free DLC.
https://store.steampowered.com/app/1385460/Drifters_Loot_the_Galaxy/