Old school shooter Serious Sam: The First Encounter (Windows) is free to download (until August 26) and keep forever, courtesy of GOG.com, a global online game retailer of DRM-free games (games that always remain fully yours, no matter what).
Serious Sam: The First Encounter Giveaway
The game is offered in the simplest of forms. There are no requirements from GOG to get the game for free other than registering on GOG.com in order to add the free product to your cart, before being able to download it straight away, or at anytime, for good. The free game can be found at https://www.gog.com/game/serious_sam_the_first_encounter.
Serious Sam: The First Encounter
In the near future, during their first interstellar travels, humans encounter a great evil that has been roaming the galaxy for the last few eons. This evil being is an incarnation of the last ancient immortals called Notorious Mental. Mental has set forth to wipe out the Human Race, just for fun, as it has with all the other civilizations in galactic history.