This says there IS 1-time DRM for each install on a different PC:
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http://www.gamersgate.com/info/faq
Can I download a game on one computer and install it on another one?
Yes, you can.
1) Copy the download file and the temp folder as they are located near each other
2) Paste on another computer that has connection to the internet
3) Run the download file and fill in the login/password if necessary
4) The installation process will start automatically, if the temporary folder is in place, since it will find the install files.
NOTE: Internet connection is required for performing the installation process. Installation cannot be made manually. It is done automatically and it requires internet connection to be performed properly.
Can I download the game on my office PC and install it on my home PC which does not have an internet connection?
No, you cannot. Internet connection is required to install games. If the target computer has slow download bandwidth, then the game can be downloaded on another computer and then transferred in any way to your original computer. There you can use them to install, but connection is needed to sign in and start the installation process.
NOTE: You should move the download file and the temporary Gamersgate folder (GamersGate temporary files) as they are placed near each other in order to install the downloaded games. Otherwise the downloader will start the download process again. Installation should be started using the download file, and it cannot be done manually from the temporary folder.
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That means if the GamersGate install-time server ever shuts down, you can't reinstall.
The GoG installs are just files, with no phone-home check.