No strings attached.
Uplay are offering the Microsoft Windows PC version of Assassin's Creed III for free until December 31, 2016! That version normally costs $19.99.
To claim your free copy, simply log into your free Uplay account, click on the offer on the homepage, and follow the directions on the offer page.
Related note: The Assassin's Creed Bronze Pack is on sale for $14.99 (75 percent off) on Uplay until January 7, 2017. That pack includes the following games:
Assassin's Creed II Deluxe Edition.
Assassin's Creed Brotherhood.
Assassin's Creed Revelations.