While browsing the web, I always close tabs using the middle-click and I'm wondering, would it be possible to close applications and windows by middle-click (Example: By clicking on the title bar) ?
Also, would it works in gnome 3 ? (Note that in the gnome Advanced Settings there is no close option for the middle-click)
If you are using GNOME 3 then this extension will solve your problem. This applies to closing applications with middle click in the GNOME 3 'Activities' Overview.
https://extensions.gnome.org/extension/352/middle-click-to-close-in-overview/
Ubuntu and Unity still depend on metacity(!) for this kind of action. So you would find all possible 'titlebar action' possibilities in gconf-editor >apps>metacity>general. Unfortunatelly (as in gnome3) there is no 'window close' option.
As there is no 'out of the box' solution for your idea, my approach would be different.
Most of your application will have a 'close' or 'quit' keyboard shortcut. That might be >ctrl< q for QUIT, or >ctrl< w for WINDOW CLOSE, or >ctrl<>shift< q to QUIT a gnome-terminal.
I would now install the software easystroke and add a mouse gesture for the given command. The same mouse gesture can have a different command, following the active window. Let's say a 'right click' and drawing a 'circle' would mean >ctrl< w for the filemanager, but >ctrl<>shift< q for the gnome-terminal.
This solution would give you a similar ease of use, as 'middle-clicking' the titlebar. Needless to say that I am using this kind of solution... ;)
Here is some video I found on the youtube... easystroke in action
The Middle click has a special meaning in Unix like systems that use a certain library. If you mark text somewhere and then click on a field that accepts text, it will paste the marked text into that field (try it in your browser). So no matter what you do, you will not be able to make the middle-click work as expected for all applications.
However, you can try mapping the middle click to a keyboard key and then assigning a keyboard shortcut to close windows.
Another possibility is using the Many Button Mouse or IronAHK.
