I don't know of anybody else has mentioned this project, so I'm posting a new topic (forum search came up with nothing). I've been keeping an eye on this project:

https://github.com/tkashkin/GameHub
Somebody mentioned it on Reddit a few weeks back and I checked it out. It seemed curious enough, but I thought it would probably end up being one of them interesting ideas that never end up anywhere. Or a simple installer, at best. Fast forward several weeks and the developer is spitting new features and squashing bugs like mad. They just added initial gamepad support. There is also using Proton for non-Steam games. And you can unify your Steam, Humble Bundle and GOG libraries into a single place.

Considering this is a 4 months project, made by a single person, I find it very, very impressive. Being able to have an unified game library has been a dream of mine for quite a while. And to have controller support - oh, boy. Only gripe I have is not being able to add install through PPA on Linux Mint 19 because of some convoluted dependency issues, but I'm not going to nitpick an aplha stage project.