The Adventure of Tree free on IG : https://freebies.indiegala.com/the-adventures-of-tree
Mido and Di free on Steam : https://store.steampowered.com/app/1691560/Mido_and_Di/

①  Cult Manager Tycoon؜, a satirical tycoon game in which you run a cult, is currently free for the next 6 days on Google Play (Android).  Here's a gameplay video؜.

②  After Defense Zone, its sequel, Defense Zone 2, is free for a limited time on Google Play (Android).  Here's a gameplay video؜.

③  Kingdom Builder؜, the digital adaptation of an award-winning board game؜, is temporarily free on the App Store (iOS).  Here's a gameplay video؜.

④  The Firm؜, a fast-paced arcade game where you work as a trader, is temporarily free on the App Store (iOS).  The optional in-app purchases let you support the developer and buy 3 additional packs.  Here's a gameplay video؜.

⑤  Sphaze؜, a beautiful sci-fi puzzle game, is temporarily free on the App Store (iOS).  The in-app purchases are optional, they're used for hints and solutions.  Here's a gameplay video؜.

⑥  Connect؜ (ad-free version), a casual puzzle game, is temporarily free on Google Play (Android).  This version doesn't contain interstitial ads and the in-app purchases are optional and useless.  Here's a gameplay video؜.

⑦  LittleBigPlay is currently giving away 4 games on Google Play (Android) :

    ▪  Colonies؜     ( Puzzle game  ∙  Gameplay؜ )
    ▪  The Hearts؜     ( Puzzle game  ∙  Gameplay؜ )
    ▪  Over The Bridge؜     ( Arcade game  ∙  Gameplay؜ )
    ▪  Word Search Games؜     ( Word game  ∙  Gameplay؜ )

⑧  The following games are free for a limited time on the App Store (iOS) :

    ▪  Alice Trapped Beyond Wonderland؜     ( Adventure game  ∙  Gameplay؜ )
    ▪  Tiny Orchestra؜     ( Educational game  ∙  Gameplay؜ )
    ▪  Vive le Roi 2؜     ( Puzzle-platformer  ∙  Gameplay؜ )
    ▪  Vive le Roi 3؜     ( Puzzle-platformer  ∙  Gameplay؜ )
    ▪  Hugo Hup؜     ( Platformer  ∙  Gameplay؜ )
    ▪  Kinecto؜     ( Arcade game  ∙  Gameplay؜ )
    ▪  Cosmic Frontline AR؜     ( Strategy game  ∙  Gameplay؜ )

I apologize if this has been mentioned already, but

The Elder Scrolls 1: Arena

and

The Elder Scrolls 2: Daggerfall

free on steam.

To add to y our library just click play game and then cancel out of the install.

They have been available for free for years on Bethesda's site without the Steam DRM and can be played offline without signing in to Steam using DOSBox. They used to be available for free here on GoG, but seem to have disappeared from the catalog. I could be remembering wrong, but I think Arena was released with Skyrim or one of the expansions and Daggerfall was released with one of the spinoffs.
https://elderscrolls.bethesda.net/en/arena
https://elderscrolls.bethesda.net/en/daggerfall

They never were available for free on their own here. But you still get them as a bonus goodie when you buy any game from Bethseda.

You can add Fallout Shelter, The Elder Scrolls: Legends and Wolfenstein: Enemy Territory to that list, along with the Fallout 4: Creation Kit and the Skyrim Special Edition: Creation Kit. They always have been free from the Bethesda Launcher and from Steam...

Indiegala:

Age of Steel: Recharge

Epic Games:

Terraforming Mars - Link

From Asmodee Digital, this is a turn-based strategy game for space lovers!
Where you compete with others to transform Mars into a habitable planet!
Single player and multiplayer modes are available
Build cities, Industrialize, and race to control Mars before others!

Just one game this week

Next time: Prey and Jotun: Valhalla Edition

Control Craft 3 is the new freebie at Indie Gala.

①  57 ⁰ North؜, a story-driven adventure game with multiple endings, is currently free on both Google Play؜ (Android) and the App Store؜ (iOS).  This game is compatible with the Merge Cube؜ to enhance the immersion.  It seems to be permanently free right now, but it was $2.99 a few days ago.  Here's a gameplay video؜.

②  Warlords Classic؜, the official port of a turn-based strategy game available on GOG؜, is temporarily free on the App Store (iOS).  The mobile version comes with 3 maps (Illuria, Erythea and Reldaria), and 28 additional ones are available via in-app purchases.  Here's the gameplay trailer؜.

③  EGProject is currently giving away 4 first-person horror games on Google Play (Android) :

    ▪  The House؜     ( Gameplay؜ )
    ▪  Stone Of Souls 2؜     ( Gameplay؜ )
    ▪  Dead Bunker 2 HD؜     ( Gameplay؜ )
    ▪  Dead Bunker 4؜     ( Gameplay؜ )

④  D7؜ (ad-free version), a puzzle game based on dominoes, is temporarily free on Google Play (Android).  This version doesn't contain interstitial ads and the in-app purchases are optional and useless.  Here's a gameplay video؜.

⑤  Trivia Master؜, a quiz game with over 20,000 questions, is temporarily free on Google Play (Android).  The game can be played offline, and the reward ads and in-app purchases are avoidable, they're used by the hint system.  Here's a gameplay video؜.

⑥  The following games are free for a limited time on the App Store (iOS) :

    ▪  8bitWar: Netherworld؜     ( Strategy game  ∙  Gameplay؜ )
    ▪  Dadi؜     ( Puzzle game  ∙  Gameplay؜ )
    ▪  7 Stories؜     ( RPG  ∙  Gameplay؜ )
    ▪  Match Attack؜     ( Match-three  ∙  Gameplay؜ )
    ▪  Monsterz Minigames Deluxe؜     ( Mini-games  ∙  Gameplay؜ )
    ▪  Talk About The Monster؜     ( Interactive book  ∙  Gameplay؜ )
    ▪  Animal Class؜     ( Trivia game )

⑦  The following games are free for a limited time on Google Play (Android) :

    ▪  Defense Zone 3؜     ( Tower defense  ∙  Gameplay؜ )
    ▪  Word Search Challenge؜     ( Word game  ∙  Gameplay؜ )
    ▪  Word Cage؜     ( Word game  ∙  Gameplay؜ )
    ▪  Broken Words؜     ( Word game  ∙  Gameplay؜ )
    ▪  Broken Sentences؜     ( Word game  ∙  Gameplay؜ )
 

☆  Royal Defense؜ (DRM-free), a tower defense game similar to Kingdom Rush, is temporarily free again on Indiegala.  Here's a gameplay video؜.

☆  The English version of Restart: New Beginning (DRM-free), a visual novel with multiple endings, is also free on both Indiegala؜ and itch.io؜.  Here's the official gameplay trailer؜.

Epic Games:

Prey - Link

Prey Returns! One of my favourite games of all time!
Prey is a FPS and action-adventure game made by Arkane Studios.
You are Morgan Yu (can choose female or male in-game).
You awaken aboard Talos I, a space station orbiting the moon in the year 2032.
You and your brother are operating a company equivalent to NASA in real life.
You go through a series of tests only for something to go awry.
The alien specimens in the experimental lab rebel and attack everyone!
What will you do? Which side would you choose? Fate of humanity rests in your hands...or gloo cannon.

Side note: There are also fun Easter eggs and special secret games inside the game.
Highly recommended for RPG and board game lovers to explore those side missions!
Take your time and explore everything to get the most out of this game and the mystery behind Talos I.

Mooncrash DLC is included

Jotun: Valhalla Edition - Link

Jotun, made by Thunder Lotus, is a hand-drawn action-exploration game set in Norse mythology.
Also a repeat from Epic Games.
In Jotun, you play Thora, a Viking warrior who died an inglorious death
You must prove herself to the Gods to enter Valhalla. Impress the Gods!

Redout: Enhanced Edition - Link
Redout is the fastest game ever made. If you can handle it.
It's not about the numbers you see on screen, it's about the vibrations,
the landscape and buildings flying by, the high-speed collisions, the effects, the sounds, the immersion:
everything is meant to feel like you're going FAST.
Made by 34BigThings SRL.

This is a new giveaway!

Next time: Mystery Game!

Edit: Formatting and clarification regarding repeats

The Lightweight Fighter Pack DLC of World of Tanks is free on steam (base game is F2P) : https://store.steampowered.com/app/1662502/World_of_Tanks__Lightweight_Fighter_Pack/

Dangerous Lands free on Indiegala.

https://www.epicgames.com/fallguys/en-US/free-for-all-pre-registration

everyone who launched the game before it goes f2p receives a Legacy Pack with cosmetics and a free Season Pass for Season 1

The Steam version will be delisted like Rocket League, existing players can play through Steam, new players only through Epic.