Altitude0:Lower & Faster
Dovetail Games Fishing
The Room
Season Match 3 - Curse of the Witch Crow
Beware Planet Earth
Max: The Curse of Brotherhood
Jacob Jones and the Bigfoot Mystery Bundle
Wolfenstein: The New Order ROW
BattleBlock Theater
Red Faction Guerrilla
Red Faction 2
Red Faction
Red Faction: Armageddon - Path to War DLC
DiRT 3
Battlefield Bad Company 2 Standard Edition
Thief Challenge Map DLC ROW
Thief The Bank Heist DLC ROW
Thief Booster Bundle DLC ROW
ENSLAVED: Odyssey to the West Premium Edition ROW
Resident Evil 6
Postal 2 Complete
Next Car Game: Wreckfest - Digital Deluxe Edition Upgrade
Sleeping Dogs: Definitive Edition
Slender: The Arrival
Gone Home
Halo: Spartan Assault
Super Meat Boy
Among the Sleep
Car Mechanic Simulator
Terraria
ORION: Prelude
Saints Row IV Game of the Century Edition
3DMark Advanced
Alien: Isolation
Toybox Turbos
Portal 2
Five Nights at Freddy's 2
How to Survive - Storm Warning Edition
Dwarfs
Robotex
Broken Sword 4 - the Angel of Death
FaceRig
Microsoft Flight Simulator X: Steam Edition
So basically if a Dev doesn't get enough interest (money) for their game they can just drop it without fear of refunds etc.
As always - buyer beware!
I guess you could trade cards a bit like the stock market. In theory you could make money, but it would be pretty poor with the trading fees.