PC Gamers is now offering all 5 games till August 3rd. Normally you can go to their website and just get the codes, however it may or may not work. I tried it when they started the campaign and after few tries I just gave up. Now however there is a simpler way to do it.
Basically go here for games:
http://woobox.com/vriikh -> SpaceChem
http://woobox.com/828jhg -> Dino D-Day
http://woobox.com/aiwwwi -> Gun Monkeys
http://woobox.com/o36sxt -> Really Big Sky
http://woobox.com/wczo6x -> GTR: Evolution
Use an ALT Facebook Account or a real one, it doesn’t matter. Like their page, and then enter your e-mail (they don’t really send codes via e-mail btw).
Once you press submit you will see the codes but before that, you will be asked to install an app called Coupons, simply let it install but in permission, make it CUSTOM and then select ONLY ME.
Once done, get all the codes. After that, go to:
https://www.facebook.com/settings?tab=applications
Remove Coupons APP and you’re done.
But make sure to redeem your keys via Steam Client (doesn’t work via Web store). You can redeem keys anytime, there is no time limit but it’s better you redeem them anyway.
Hope this helps.