Shadow Complex Remastered is a free Download for PC until Dec. 31st on the Unreal website.
If you've not played it's well worth checking out. It's a Metroid style game, but one of the better ones. You need to download the launcher and then pick it up from there. Find it by clicking on the Unreal logo on the top left corner. Fair warning that you'll have to install the Unreal Launcher client, register, then get the game from there, or you could just wait and buy it early next year from Steam, on the PS4, or Xbox 1. It's a free game, and an awesome one at that, so it's kind of worth dealing with installing the Unreal client even if it's just temporarily.
There are some neat betas and stuff available through it as well if certain types of games are your fancy. It's not like downloading the Steam client as it's really a dev console for the Unreal Engine. The marketplace mostly sells assets for building games using the engine and it's how Unreal handles beta and alpha testing.
This is the full release of the Remastered version of the game by the way, not a demo or the old version being given out as a promo. They're literally giving it away to PC players to download and play early this month.
EDIT: Just to be clear, based on how they've been talking about this, I'm 99% sure this is a timed trial. You don't get to keep the game forever and it deactivates at the end of the month. It's sort of like a free month long rental and not a copy you get to keep forever.
That said, this is plenty of time to beat this game more than once even if you're not constantly playing it during the month. It can be done in a day or two at most.