With Ubuntu 18.04 I started to love the Software center (SC) since it is super reliable and with the ability to also have snaps and flatpaks inside the same SC makes it an amazing place where you can find pretty much any piece of software. But one type of software is missing from there and it is appimage. More and more apps are getting built in that kind of format and with the use of App Image Launcher https://www.appimagehub.com/p/1228228 and App Image Store https://www.appimagehub.com it makes it super easy to install and manage appimages. Just click on any and that's it, it "installs" and adds them to the Gnome Apps. Right click any and "remove" and they are removed. They can also be updated in the same simple manner.
Now I'm wondering isn't there any plugin for Ubuntu SC to add appimages as well? That would be so amazing :)
Unfortunately, there is no AppImage Plugin (support) for Gnome Software/Ubuntu Software Centre. A point of hope is that some private/third party developers like https://github.com/AppImage/AppImageKit/issues/244 are working on it. We may expect the AppImage support in GS/SC soon in the future.