Alright. I saw a new list here ([Steam] List of paid-now-free games of 2019 (FreeOnDemand)) and thought to my self: why don’t I go through the list to add some more items to my post.
Well, turns out that took me several days for reading those reviews and watching videos.
Anyhow, I’m finally here.
Given that these games are now free, I did lower my expectation when making the selection. But I was still surprised by the plethora amount of hidden gems Steam has to offer. 
Beware that this is gonna be a long list to load in. And as always, feel free to share your thoughts on these games.
(Courtesy to @Modoc. This one seems pretty slick to me even in these days.
)
https://store.steampowered.com/app/376110/Black_Island/
https://store.steampowered.com/app/1085150/Golf_Defied/
https://store.steampowered.com/app/733870/King_of_the_Eggs/
https://store.steampowered.com/app/655940/Elo_Hell/
https://store.steampowered.com/app/989040/After_Hours/
https://store.steampowered.com/app/761290/Sink_or_Skim/
https://store.steampowered.com/app/952330/Blackfoot_Burrows/
https://store.steampowered.com/app/237870/Planet_Explorers/
Have a good one 
Came across some used-to-be-paid games and they might be interesting for fans of different genres.
So here we go:
https://store.steampowered.com/app/330450/Runes_of_Brennos/
https://store.steampowered.com/app/713540/Neptunian_Donut/
https://store.steampowered.com/app/756100/Curse_of_the_Old_Gods/
https://store.steampowered.com/app/458660/The_Slimekings_Tower/
Hope there will be something of your interest. 
P.S. This seems to be handy for those multitasking geniuses:
https://store.steampowered.com/app/834170/Chameleon_Video_Player/