I'm wondering if it's possible to group two or more windows in Xfce and make them act as a single window.
I mean, I use multiple git cola Windows for multiple repo. I'd like to glue these windows side by side and move/resize/reduce as a single window.
Any idea?
No, this is not possible with xfwm4. If you want such a feature use a tabbed window manager like twm (I think kwin can do this, too). See https://wiki.xfce.org/howto/other_window_manager for informations how to switch your WM.
I was browsing the internet and trying things for quite a while. Finally, I managed to reach what I think you asked.
Using Xfwm4 on Linux Mint 17.3 Xfce, I ended up on the webpage http://docs.xfce.org/xfce/xfce4-panel/start which links to the page for "Windows Buttons" on http://docs.xfce.org/xfce/xfce4-panel/tasklist. On the screenshot shown there, you can see the option "Window grouping" where "Never" is chosen. If this is changed to "Always", two or more windows are grouped like we know it from e.g. MS Windows.
The question is now how to reach this menu. "Window Buttons" is the standard item in the panel to switch between different windows. The difficulty now is to right click on this item in the panel without right-clicking on a specific window. If the space is not enough, just navigate to the "Panel Preferences" and increase the "Number of Rows" until you find some space in the "Window Buttons" item. Then right-click this space and choose "Properties". A window like the screenshot in the link above pops up and you can change the desired option.
for terminals, you can use terminator, which basically splits the terminal window into multiple ones with ctrl-shift-e and ctrl-shift-o.
For windows in general, i'm not really sure how that would work.
You can use tabbed for applications that support Xembed
