Apps with 'Flatpak' feature

elementary OS is a free, fast and aesthetically pleasing operating system based on Ubuntu .

Games library manager.
Supports: Steam, GOG, Humble Bundle, Humble Trove, Wine and RetroArch
.

Endless OS is a Linux-based operating system which provides a simplified and streamlined user experience using a customized desktop environment forked from GNOME 3.

App Outlet is a Universal application store inspired by the Linux App Store online service. It allows you to easily search and download [W.I.P] applications that run on most Linux distributions. It currently works with AppImages, Flatpaks and Snaps.

Flatseal is a graphical utility to review and modify basic permissions from your Flatpak applications.