There's a Calibre plugin[1] that does it.
If you really care about ebooks that you purchase, I highly recommend installing this plugin. It automatically strips DRM off books you download and open with Calibre.
And keep a back-up of the (DRM-free) books somewhere that's not Amazon / a cloud. Because a cloud is simply a computer that you do not own.
[1]http://www.geoffstratton.com/remove-drm-amazon-kindle-books
https://gizmodo.com/its-perfectly-legal-to-tell-people-how-t...
In fact, I believe in some jurisdictions it's actually legal: since you bought it, you're allowed file and sandpaper it to make it actually work.
Can you imagine anybody in the industry saying “That’s enough money” today?
It is the game publishers that choose to use steam drm. Often the same publishers publish on GOG without the drm (since gog, admirably, does not offer a drm option to them), but it is not steam that is forcing the drm on you. Your issue is with the game publisher.
I don't see any compelling reason for me to prefer them over Steam, anymore.
Honestly, if I'm going to fight against my software, I might as well be pirating.