Flatseal is described as 'Graphical utility to review and modify basic permissions from your Flatpak applications' and is an app. There are five alternatives to Flatseal for Linux, Flatpak, Flathub and Windows. The best Flatseal alternative is Warehouse, which is both free and Open Source. Other great apps like Flatseal are Flattool, Concessio, Permissions Reporter and jdPermissionStoreEdit.
Warehouse is a versatile toolbox for managing flatpak user data, viewing flatpak app info, and batch managing installed flatpaks.
Flattool is a command line script designed to improve user experience with flatpaks. It streamlines flatpak management tasks, making them more efficient and user-friendly.
Permissions Reporter allows you to quickly validate the current security posture of entire local and/or network file systems at once. All with multiple export formats, command-line support, built-in scheduling, and much more.
Flatseal deals with permissions for applications (specifically Flatpak programs) whie Permissions Reporter doesn't handle Flatpak programs at all and is aimed instead at networked file systems.
They do completely different things.
jdPermissionStoreEdit allows you to directly view and edit the Flatpak Permission Store. This makes debugging easier when you are working with it (e.g. if you are developing an app to manage Flatpak permissions).
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Flatseal lets you manage permissions and nothing else. Warehouse does everything EXCEPT permissions.