I share games with my sister on steam,
We can have the same games and get the achievements of each one, with the only limitation that we cannot play the same game at the same time.
I like that
now I want to know if i can do the same on GOG ?
I want to share some of my games with her, but she wants to know if she has the same limitations and if she can get the achievements from the games I share with her like on Steam.
That's possible ?

You can both play the games if you're living in the same household, but I'd imagine it would be a single set of achievements (I don't use the client and always turn off achievements). If you're not living in the same household then she should purchase her own DRM free copy.

You can "share" on GOG just as you can on Steam in a legal sense, as both services prohibit sharing in their Terms of Service.

From the Steam Subscriber Agreement:

C. Your Account

When you complete Steam’s registration process, you create a Steam account ("Account")...You may not reveal, share or otherwise allow others to use your password or Account except as otherwise specifically authorized by Valve. You are responsible for the confidentiality of your login and password and for the security of your computer system.

From the GOG User Agreement:

3.3 Your GOG account and GOG content are personal to you and cannot be shared with, sold, gifted or transferred to anyone else. Your access to and use of them is subject to GOG’s rules which are set out here, as updated or amended when necessary.

Your GOG account and content are for you only – there are rules about how to use them (see opposite).

If you are happy to disregard Terms of Service, then GOG offers more flexibility since it provides offline installers that you can run on as many computers as you want. If you want to play by the rules however, you and your sister should have separate accounts on both services (and this will apply to pretty much any other game store too).

That is not an accurate statement, since Steam has a "Family Sharing" feature, and GOG does not have any equivalent feature.

So the correct answer to the OP's question is no, you cannot.

Not mentioned in the Steam Subscriber Agreement linked to above.

shame
It should be an option to be able to share some games like on Steam.
thanks

Because it doesn't violate that statement above. You don't Family Share by giving anyone your password or access to your account.

In reality you can easily do whatever you want, because the games here, single player at least, are DRM-Free.

That said it is not really legal to share beyond your household, and certainly not give another person your username and password to your GOG account.

But let's say you have more than one PC you own, you can quite legally install your GOG games on those PCs. You could then effectively lend one of those PCs to your sister. Just like if she came and visited you, it would not be illegal for her to play a game from GOG on your PC. Proving ownership of the PC would be the thing though. But honestly, who is going to be going around doing that.

GOG and those who provide games to GOG, rely on customer trust, unlike Steam in many instances where DRM is involved.

Nothing really stops you, even though most EULAs will say you shouldn't.

Sorry, but are you saying SFS allows you to play different games from your library on different computers at the same time, or are you using offline mode to get around the library lock restriction?

on steam
I can share my games with my family members.
I just can't play the same game at the same time
she can have the game installed on another pc
and she can unlock all the achievements and have her own save

Reusing DRM to make it a 'Library checkout' system. Even if you have all the files on your computer(s).

Well to make it easy, you can share games if you share either your hardware with the game installed, or you share the installer. (I put my games accessible on the network so all machines could install it if i wanted). As for locking the game, it's kinda pointless. If i have 300+ games, what's the odds that the same game would be played by someone else as well as you? And if it was, does it even matter?

Other than say Terraria or some other multi-player game (Neverwinter Nights?) which you might want to play at the same time with your family, the DRM locking/sharing doesn't do anything. I'd rather not be in the mood to play a specific game, and then 'OOPS Your sister is playing game X so you can't boot it'... Just install the game on the shared machine or their machine and call it good.

That is correct. There is no mechanism for her account to gain access to a game that she hasn't bought, or for her to earn separate achievements. However, she could play the game on her PC if she wanted to because the games are DRM-free and require no client or online verification of any kind for single-player games. The saves, then would be local.

Thanks
so, I will buy some games on steam :T