You can now link your Steam account to GOG to get DRM-free backups.

[AlchemistHohenheim]

For select games only, the eligibility of which will cycle in and out:
https://www.gog.com/connect

HOW DOES GOG CONNECT WORK?

To connect your library with GOG.com, sign in to your active Steam account via this page. NOTE: Make sure your Steam Privacy Settings & Profile Status are set to public.

You'll be able to permanently import all the games listed below to your GOG.com library – assuming you own them. The eligible games are limited-time offers made possible by participating developers and publishers, so stay tuned for more games to come.

You can connect only one Steam account with your GOG.com library. This process is permanent – choose wisely!

Currently eligible games as of 6/13/2016:
Bit.Trip Runner
Braid
Breach & Clear
Breach & Clear: Deadline
Broken Sword: Director's Cut
FTL: Advanced Edition
Galactic Civilizations III
Mount & Blade
Project Zomboid
Saint's Row 2
Shadowrun Returns
Surgeon Simulator 2013
Sherlock Holmes: Secret of the Silver Earring
The Incredible Adventures of Van Helsing: Final Cut
The Witcher: Enhanced Edition
The Witness
To The Moon
Trine Enchanted Edition
Two Worlds
Unreal Gold
Unreal Tournament GOTY
VVVVVV
Xenonauts
Defender's Quest
Door Kickers
Kona

No games are currently eligible for redemption. Will update when some are.

[TheNecroswanson]

That's pretty dang awesome!
Can't wait to see if they get all of my games on there.

[HatKid]

This is super cool! I finally got motivated to make a GOG.com account, and I hope that eventually Trails in the Sky FC ( 'cuz I still haven't bought SC, and I haven't finished FC yet.) gets added to this. I've always mildly regretted buying Trails in the Sky on Steam and not GOG because of all the neat extras that come with the GOG release.

[Telamon]

I honestly don't know if I'll bother to link any of my games, but I do love gog. Rah rah fight the steam monopoly and all that.

[Dustinvgmaster]

Wow, this sounds pretty rad, honestly. Thanks for the heads up.

[Drei]

Unfortunate that so few are on the list right now, but I'm probably going to switch to only purchasing games on GOG at this point on. I'm not very happy with the idea of Steam's DRM keeping my games unusable eventually, and I believe GOG provides previous patches for games too for all your mod/bug related problems.

[AlchemistHohenheim]

FYI, the batch of games currently listed in the OP expires in about 20 hours. So if you already have any of them on Steam, and want free GOG copies, you need to link your account and redeem them before approximately 9AM EDT tomorrow.

Besides that, they've added:
Door Kickers
Defender's Quest
Kona

Like the first batch, these will be available for 5 days before expiring.