My favorite co-op game in years is on sale for $3 in the Steam Summer Sale

pcgamer.com:

One of the best co-op games, and one of oh-so-few stealth co-op joints around, Styx: Shards of Darkness, is 85% off (just $2.99) for another couple days. With the Steam Summer Sale not quite closed, it's not too late to toss some pocket change at another couple games. Better yet, talk a friend into playing with you.

I routinely cycle back through my whingeing that co-op campaigns just don't exist like they used to and Styx: Shard of Darkness was the answer to my grievances when I picked it up a couple years back. It's a proper stealth romp with large levels to dissect by picking off guards and avoiding combat with darkness and crawl spaces. All you've got to suffer for it are some bottom-shelf scatological jokes from a snarky goblin. 

If you got burned by the not-stellar creepy little guy stealth in The Lord of The Rings: Gollum, this should be your next port of call. We gave it a nice 79% in our Styx: Shards of Darkness review and despite how easy I find it to recommend it's maintained a shadowy, lesser-known status.

You can play it solo if you prefer but it's a grand time in co-op. As Styx and Clone Styx, you and a pal both get to unlock your own tree of skills to specialize in proper soundless stealth, traps, alchemy, and tracking enemies. You can stick close together for some great double kill setups or split up to pave the way for each other by dousing lights or taking down armored guards. It was truly the best bit of whooping and hollering over clinch move moments I've had with a friend in years.

Styx actually gets down below $5 several times a year, but this $2.99/£2.69 is the lowest it's gotten. It's a real breezy 10-ish hours at a price that's really easy to wheedle your co-op partner of choice into trying. The