“Ubisoft has announced it’s extending its Happy Playdays giveaway and adding Watch Dogs to the selection of PC games available for free for a limited time.”
The Ubisoft site:
https://www.ubisoft.com/en-gb/event/happy-playdays-2017/#207315645
Didn’t they just give away all of these recently?
Yup!
Watch Dogs on Nov. 6th, 2017
Black Sails on Dec. 11th, 2017 and
World in Conflict on Dec. 4th, 2017.
Still, I’m happy because for some reason I missed Watched Dogs or something, and now I can finally play it!
So thanks so much for sharing this here as well, of course! 
Between all of us here, we cover almost all the giveaways.
so is it completely free, for is it a trial like how its done on steam
Yes. You have to have their game manager installed and have an account with them…just like your Steam or Origin games.