Released

The Stanley Parable

The Stanley Parable is a first person exploration game. You will play as Stanley, and you will not play as Stanley. You will follow a story, you will not follow a story. You will have a choice, you will have no choice. The game will end, the game will never end. Contradiction follows contradiction, the rules of how games should work are broken, then broken again. This world was not made for you to understand.

Trainz Simulator 12

Trainz Simulator 12 is a 3D railroad simulator that uses DirectX or OpenGL with multiplayer and the option of downloading 3rd party tracks, railcars, and objects.

Jazzpunk

Jazzpunk is a comedy adventure set in an alternate reality Cold War World, plagued with corporate espionage, CyberCrime, and sentient martinis. Gameplay is inspired by spoof comedy films and cartoons of yesteryear, with a focus on weird gadgets, exotic locales, and open-world style exploration.
(source: steam store page)

Marathon

Defend the titular colony ship from alien boarding parties in the first game in Bungie's Marathon trilogy.

Rescue: Everyday Heroes

Do you have nerves of steel and a calm head in times of danger? Then you can join one of the most respected careers in the world in Rescue 2013 Everyday Heroes, from Excalibur’s emergency services PC game range. Rescue 2013 Everyday Heroes is the first fire-fighting simulation for PC & Mac to include genuine British fire engines and ambulances as well as their continental counterparts.

In this fire-fighting simulation game you’ll be rescuing people trapped in car crashes, dousing the flames of burning buildings and even providing emergency medical care to the injured.

Spelunky

Upgraded and expanded remake of the popular freeware game from 2009.

Spelunky Classic

Explore mysterious caverns to collect treasures while avoiding traps and monsters.

Spelunky is a freeware game first released in 2009; it was renamed to Spelunky Classic following the release of an enhanced commercial version in 2013.

Unepic

Embark on a strange adventure in a vast castle with gameplay inspired by the Castlevania series.

Mark of the Ninja

In Mark of the Ninja, you'll know what it is to truly be a ninja. You must be silent, agile and clever to outwit your opponents in a world of gorgeous scenery and flowing animation. Marked with cursed tattoos giving you heightened senses, every situation presents you with options.
(source: steam store page)

Contract J.A.C.K.

Trained to survive. Paid to kill. Explore the dark side of the No One Lives Forever universe as John Jack, a rugged anti-hero in the services of H.A.R.M. The legendary chief assassin for H.A.R.M. organization has given Contract J.A.C.K. a mission--whether he wants it or not. An Italian criminal organization has plans to take H.A.R.M. down and Contract J.A.C.K. must stop them. In doing so, players contend with deadly enemies and survive against ridiculous odds to complete the mission.