Text-heavy RPG Torment: Tides of Numenera is free to play until Sunday, and if you want to play it beyond that then it's on sale for equal to its lowest ever price.
The 60% price cut means it's just $18/£14, which is a damn good deal. Both the free weekend and sale are on Steam, and the sale ends on Monday.
If you've never played Torment and you're a fan of old-school isometric RPGs, then you should really give it a try. As Chris said in his review, it captures the magic of the original Planescape: Torment—perhaps the best RPG of all time—by placing thought over action. Combat features, but you can play the whole thing non-violently, talking your way out of tough situations.
There's a lot of text, and you'll get the most out of Torment if you dive into the reading, which will help you make connections between different storylines. If you're looking for a loot-heavy game or something with lots of party strategy, then this isn't it. But otherwise, it's free, so why not?
It also had a free weekend back in October, so it's likely to have another at some point.