Magrunner: Dark Pulse is currently available for free as part of GOG.com's ongoing .
Of course, that's not the only offer on the table; there's currently 30 different bundle deals available, along with a number of flash sales.
Developer Frogwares has an action/physics title in the vein of Portal for us on PC. It's called Magrunner: Dark Pulse, but don't think some quirky AI with snappy quips awaits you. This is much darker and moodier.
It prefers to manipulate physics through head-scratching puzzles in a more psychologically scarring way. It sees technology confronting the 'Cthulhu Mythos', describe Frogwares.