https://www.gog.com/en/mods
Mods are an essential part of video games preservation, allowing you to relive your favorite stories in countless possible ways. Mods management, however – is not for everyone. Digging into game files, installing requirements, restarting the game thousands of times, making it crash every time... But no more. With GOG One-click Mods, newly introduced seamless mod integration on GOG, you can freely browse, install, and play, faster and easier than ever!
GOG One-click Mods is a curated selection of premium mods, available on GOG and directly packed with the game for the smoothest installation.
I honestly think this is a great idea on their part, especially if they work closely with the mod authors.
I have played the Heroes III mod curated by GOG and it is awesome. I loved how easy GOG makes it to install mods.