Dungeon Riders is quite a useful, popular free computer game available only for Windows, which is part of the genre PC games by category PC gaming with subcategory Adventure. It has received 19,000 downloads in the past year, and in the last seven week it had 13 downloads. I would say that more people play Dungeon Riders on other platforms than on Windows, but it is still a very enjoyable and addictive game, if you like its cute fantasy theme and fast-paced action.
Dungeon Riders is an over-the-shoulder browser-based action-adventure game where you play as one of the new characters, named Rider, a member of an elite special force called The Order of the Stick. Together with his two other comrades, he has to defeat all the dungeon Riders who have invaded the world! The story is about a young woman called Lyra, who thanks to her magical powers is able to turn the tide of the battle against the Dungeon Rider's armies, using her pyrotechnic knowledge to create portals that allow them to pass through the dimension of not-terraximensional spaces. The game itself takes place in the realm called the Land of the Deceit, where magic is the primary resource used by the human race to fight wars.
If you are looking for free PC game download sites, try searching the relevant keywords on any search engine. Note that I have not tested this game, so I cannot vouch for its accuracy or completeness. Be prepared to lose your account, as with any PC game that requires that you register for a paid version to unlock some of its features (such as the in-game tutorial or the ability to customize your character). However, if you like what you see, you can probably justify paying the price.