This has been free before and is now free again. It has trading cards that can be sold.
http://store.steampowered.com/app/303390/
The usual applies:
How to get the key:
IG has got some requirements to be fulfilled before you can get the free key. Those are:
Steam account linked to your Indiegala account
Steam account is a member of the IG Steam group
Steam account must be set to public
The procedure to get the key itself has remained the same:
click on Claim Giveaway button
log in to your IG account
do the captcha
click on the "Claim Free Copy" button
do captcha again (if necessary)
claim your key in your IG account (under IG Giveaways).
redeem key in Steam client
Enjoy!