XDG-App is the GNOME-backed design for sandboxed applications to allow third-party applications to better work across multiple distributions and for running applications with minimal access to the host.

XDG-App is designed around cgroups, Wayland, SELinux, namespaces, and more for delivering a modern Linux sandbox'ed experience. If this is your first time reading about XDG-App, see the GNOME Wiki for more details.

Red Hat's Alexander Larsson who has been heavily involved in the development of XDG-App has written a set of blog posts about building for XDG-App.

If you are interested in building sandboxed apps, see this blog post as part one followed by part two.