Awww yeah!
The legendary MDK is available for free on GoG.com. All you need to do is sign in, click on the get it for free button in the banner on the front page, and it’ll be added to your library. But you have to get on it, since it’s only available for the next 38~ hours.
MDK is a legendary third person shooter made by Shiny Entertainment back when they still made spectacular, creative stuff. You definitely want this in your library. Also, as you may have noticed above, the name was pretty much just a massive Demolition Man reference.