GoG.com DOSBox games start the DOSBox executable with some configs as parameters. You will have to do the same when adding the shortcuts to Steam.
First of all, pick your game. I will pick Ultima Underworld 1 because I have it installed. Right click on the desktop shortcut generated by the installer (if you don't have it on your desktop anymore, check the game's installation folder, there is one there; mine is called "Launch Ultima Underworld 1"), and see its properties:
![enter image description here](https://i.stack.imgur.com/4iJr1.png)
The shortcut's target is what matters to us. Copy everything in there, and keep it for later. In my case, the full field looked like this:
"F:\GOG Games\Ultima Underworld 1 and 2\DOSBOX\DOSBox.exe" -conf "..\Ultima Underworld 1\dosboxULTIMA1.conf" -conf "..\Ultima Underworld 1\dosboxULTIMA1_single.conf" -noconsole -c exit
Go to Steam, click on Games
in the top menu, then on Add a non-steam game to my library
. Once the game list window appears, click on browse. Find the DOSBox executable that's being used by your game. In my case this was at F:\GOG Games\Ultima Underworld 1 and 2\DOSBOX\DOSBox.exe
. Add that as a game.
Once done, find the game you added in your games list. Right click on it, then click on Properties
. You will see a Target
field in the newly opened window, with the path to your DOSBox.exe and nothing else. Replace everything in that field with the original shortcut's target that you copied before.
![enter image description here](https://i.stack.imgur.com/9hrw5.png)
After this your game should run normally when launched by Steam.
Checking on Steam, you cannot currently (as of 19/05/15) retrieve a CD key for the game. I cannot speak for Origin purchases, but it seems likely to be the same if utilizing the Origin infrastructure / client.
This might change in the future, but based on the previous systems (basically, entering CD keys into GoG here), it seems that it's not possible. Additionally, the interface linked above doesn't mentioned The Witcher 3.
Best Answer
Good Old Games doesn't usually re-write Windows games for OS X; it just wraps them in a .app with Wineskin and then puts that file alongside the necessary files for running it on OS X, and packages the whole thing in another .app file.
So to get to the saved-game files on GOG's OS X version of Wizardry 8, you have to:
This save folder has your good old .SAV and .CHAR files which can be moved to the same location on another Mac computer.
It looks like I could even move .SAV and .CHAR between Windows and OS X copies of the game, since GOG doesn't modify the Wiz8.exe that actually runs them. This makes sense, given the Wizardry franchise's history of porting old campaigns into the next game in the saga--and the Wizardry community's tenderly cherished vision of a new Wiz game being released in some glorious future.