Add it before May 27, keep it forever! A mobile puzzle game with interactive objects, cryptic clues, and codes to decipher.

https://store.steampowered.com/app/1507190/Machinika_Museum/

Add it before March 13th to keep it forever! A strategic roguelite very similar to its predecessor, Bomber Crew.

https://store.steampowered.com/app/1176710/

Add it, keep it forever before February 19th! A game creation tool that's designed many popular titles like Omori, To The Moon, Ara Fell, and OneShot. If you have any interest in making games, now's the perfect chance to try it out.

https://store.steampowered.com/app/235900/RPG_Maker_XP/

Add it now, keep it forever before October 13th! A solid co-op puzzler that's intended to be played with a friend over voice chat.

https://store.steampowered.com/app/2296990/We_Were_Here_Expeditions_The_FriendShip/

SEGA is giving away a free Steam key for Bass Fishing, if you follow the directions in the link below. Note, the reward is not delivered until the promotion ends (Aug 1st)

EDIT: Steam keeps hiding/deleting this announcement due to URL filtering. You'll have to type it out yourself:
games DECIMAL sega DECIMAL com SLASH bassfishing SLASH

https://store.steampowered.com/app/71240/SEGA_Bass_Fishing/