Heroic Games Launcher is truly becoming one of the best game managers available for Linux. Not only does it support Epic Games, it's just expanded to cover GOG too.
For the new GOG support, Heroic is able to download games using the Galaxy API (Windows and macOS) and for Linux you can use the offline installers that developers put up. It also supports DLC, you can run native Linux downloads using the Steam Runtime (requires Steam installed of course) which can fix some dependencies errors and pick languages for games that support it.
At least one account is required to use Heroic, so you can pick between GOG and Epic or use them both. There's also now a game store indicator / logo on the page for each game so you know where it's from.
The UI was adjusted for the GOG integration as well of course. There's an expandable Library list now in the left panel, you have an updated settings page to list accounts, a few bug fixes and an upgrade of Electron to v17.0.1.