A downloadable extension
This extension wraps GOG.com SDK for use in GameMaker: Studio and GameMaker Studio 2 games.
It covers the basic functionality - achievements, stats, and leaderboards, plus a few other commonly used functions.
Naming convention used here follows that of built-in Steam functions, so if you've done Steam integrations for games before, you'll have an easy enough time with this.
Note: you need to be an approved developer on GOG Galaxy Dev Portal to make use of Galaxy SDK.
Click download now to get access to the following files: