Sometimes developers have promotions where they give away their games for free for a limited time and they are yours to keep if you install them within that timeframe.
I currently have about 4 games in my Steam collection that I got for free recently due to these sort of promotions. So in this...
As part of its 30th anniversary celebration Ubisoft are giving away a free game every month for the next year.
The first title on offer here is Ubisoft's 2003 classic Prince of Persia: The Sands of Time.
The next free title will be announced mid-July.