GOG Galaxy
GOG Galaxy uses the Windows registry to store all information:
Every sub-key under the key HKEY_LOCAL_MACHINE\Software\GOG.com\Games is a game. The name of each sub-key is the ID of the game, but you can also extract the ID from one of the values.
Note that the Windows registry is case-insensitive, and you should be mindful of the differences between the 32-bit and 64-bit registry views. Do not use WOW6432Node in the key, instead use the correct registry view and let Windows do the work.
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