New answers tagged appmenu
There is a folder with "a load of app icons": /usr/share/applications.
You can install another desktop environment (for a Mac user I recommend XFCE4). A tutorial here on how to do so: http://www.howtogeek.com/193129/how-to-install-and-use-another-desktop-environment-on-linux/ Also if the fact that it's always there bugs you, you can edit it to only appear when you move your mouse to that side of the screen, or the top left ...
Most likely that's because there are multiple .desktop files for those applications in /usr/share/applications/ or $HOME/.local/share/applications/. To get the "Main Menu" app install the package alacarte.
You are probably looking for "nautilus extensions". Nautilus is the real name of the file manager used in both Unity and gnome-shell desktops. You can write extensions: as scripts (although I think this is sort-of-deprecated) In C using the gtk libraries or in various mixed languages However, for personal experience, expect to find a lot of outdated ...
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