GOG.com is described as '(Good Old Games) sells classic PC games through their download service at a low price, without DRM, and updated to run on the latest versions of Windows and other systems' and is a leading Game Store in the Security & Privacy category. There are more than 50 alternatives to GOG.com for a variety of platforms, including Online / Web-based, Windows, Linux, Mac and Android. The best alternative is Steam, which is free. Other great apps like GOG.com are itch.io (Free, Open Source), Humble Bundle (Paid), Epic Games Store (Free) and Indiegala (Paid).
itch.io gives you the ability to design a page where people can download games you have uploaded. You can optionally put a minimum price on your game (which can be 0), giving people the opportunity to pay you what they think you deserve. All files and images are hosted on itch.
Most users think itch.io is a great alternative to GOG.com.
The Epic Games store is now open, featuring games from other developers. Epic's goal is to bring you great games, and to give game developers a better deal: they receive 88% of the money you spend, versus only 70% elsewhere.
FreeToGame is a gaming platform that provides access to the best free-to-play games and MMO Games while rewarding gamers with free premium in-game loot, special offers and exclusive perks at no cost to the user!