Flatpak is the freedesktop.org software deployment and package management standard for Linux, offering a sandbox environment in which users can run application software in isolation from the rest of the system.
In Zenwalk : Flatpak is managed through the App Outlet application (https://app-outlet.github.io/).
You can also browse https://flathub.org/apps, find what you're looking for (ie : VLC) and just launch "flatpak install VLC" in an unprivileged user terminal.
Have fun !!