If you've ever wanted to make games but are intimidated by the steep learning curve of programming, this may be a good deal for you. GameMaker has always had a free version, but it has severe limitations in what you can do with it.
At the moment, if you download the free version of GameMaker Studio, it will display an option to upgrade to the Standard version free of charge. This would normally cost $50.
It's not necessarily just for beginners either, there have also been some great commercial games made with it such as the excellent roguelike Spelunky.
More details from the GameMakerBlog:
Make sure you have updated to version 1.2.1214 of GameMaker Studio. As the update is part of the beta updates channel, you may need to right click the GameMaker icon in your system tray and select the correct updates channel.
Additionally, developers can use their free Standard edition license to upgrade to the Professional edition for only $50 more. It’s likely that this is a time-limited offer, so if you’re using the free version of GameMaker Studio be sure to act quickly.
GameMaker community members expressed their delight at the offer. “I’ve been wanting to recommend Studio to friends for a long time, but the resource limits of Studio Free make the program borderline unusable,” said one user.