A few months ago, the geniuses behind Steam launched a new feature. Trading cards for games. And the best part, you can actually sell them to people - for real money!! Now, you can't "draw" the money, but you can use it to fund your gaming habits on the platform itself.
Each applicable game has a set amount of trading cards available, and by just playing the game, about half of that will randomly "drop", and get added to your inventory. You don't have to actually play, you can start the game and go out for supper or something. I've found it takes about 30 minutes or so for a card to drop.
If a game has an odd number of cards, you'll get half of that rounded up as drops (so a game with 9 cards will have 5 drops). It is also possible that the same card drops twice, or even more.
So, why collect these cards? Well, you create badges with them for each game, and the creation of the badge gives you a profile background, an emoticon to use while chatting (both which you can sell, or trade with your friends), and lately a discount coupon for another game on Steam. It also scores you 100xp points for your Steam profile. Here's a screenshot of some of mine:
All in all, it's just a ways to make your public profile a little bit more attractive, and to have some interesting emoticons to use while chatting with your friends.
The making money part is you don't have to keep the cards. You can actually sell them on the Steam Market, and name your price. Obviously the guys with the cheapest card will sell theirs first. A part of the price goes to Steam (clever fellows they are) and another part to the developer, and the rest gets added to your Steam Wallet.
One incentive to actually level up your profile, is that for every 10 levels, you get a higher chance of getting a random booster dropped - boosters contain three random cards - so far I've received 3 of them, and 1 of them actually contained a rare foil card - these are much rarer and typically sell for at least 10 times the price of normal ones, but other than looking a little bit different, they don't mean much. I've put mine up for sale :)
See my Steam profile here (feel free to befriend me on Steam, maybe we can play together sometime!)
I've crafted 19 badges so far, and it didn't cost me anything, just choose a few games and sell their cards, then with the money you make, buy the cards you need for the games you want to craft your badges for. I'm sure if you have tons of time to kill, you can actually buy low sell high and make enough to buy a DLC or two, but that would take some real commitment!
Anyway, it might seem pointless, but believe me, once you get going with it, it's very addictive hehe...