Lifthrasil: As nightcrawler pointed out: that's illegal. DRM-free means, GOG has no control over their games after the sale. Nothing would keep you from keeping the games after you have sold your account to someone else. Just download the games and play them yourself. You don't even need any client to do so.
Nezgaar: So DRM = Digital Rights Management right? What does that means? I can download and install games wherever i want (outside of gog galaxy..Like on my hard drive or flash drive) and keep them or i can burn them on disc.or something like that?
Yes, essentially it’s all about control. Either you have it, “they” have it, or there is a combination of the two. The ideal world is where you, the consumer has 100% control. This is mostly true with GOG, you buy the licence and then they give you the files to do with as you want. Other companies put various levels of control on, for instance steam has CEG which is their control module linked to their client. But they also sometimes have requirements to link to origin or uplay to run a game. These are all levels of control which take away from your position as the consumer on how you use the product.
It’s not however, just about control. You can add in monopolisation - having users tied to one system and data capture - data is more valuable than product now (Facebook is a good example).
Ultimately op the producer wants you fully and dependantly reliant on them, hence streaming is the big next thing.