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I'm not sure it's advisable to attempt to change the window manager in Ubuntu 18.04. The window manager is integrated into GNOME Shell.

You may find Rofi suitable for the purpose you describe while leaving the system's default intact.

• Rofi is available in the universe section.




• It has an installed size of 524 kB and and very few dependencies which you can see by running apt show rofi as well as by simulating its install using apt install -s rofi.




• Rofi has several functions but the one of interest here is the window switcher.

Once Rofi is installed:

• Create a folder called rofi in ~/.config.




• Run rofi -dump-config > ~/.config/rofi/config.rasi to generate a local config file which you can modify to suit your needs.




• Preview the theme you'd like to use by running rofi-theme-selector. If you want to tweak the theme further, you could copy the theme over from /usr/share/rofi/themes to ~/.config/rofi and give it a new name to avoid confusion. I like Pop-Dark and named the local version myPop-Dark. In the images posted in this answer, I've used myPop-Dark.

Usage

To demonstrate Rofi's use as an alternative to the system's Alt+Tab:

• I opened several windows including five xterm windows. (I opened GNOME terminal and ran nohup xterm -xrm 'XTerm.vt100.allowTitleOps: false' -T whatever & as based on the accepted answer in Simply set xterm title.)




• I assigned Ctrl+Win+R as a shortcut keyboard combination to run rofi -show window -theme myPop-Dark

In the image posted above, there are three columns. If you always want only the name of the application and the title of the window, edit ~/.config/rofi/config.rasi to change the commented out window-format line to

window-format: "{n}    {t}";

You can also modify the width, the height, and the location of the rofi window.

To bring the window you want into focus, use the arrow keys or your mouse pointer to highlight the entry and then press Enter.

If you have a really long list of windows, press a key that's unique to the window you want to filter out all other windows. If that's not possible, filter the entries by typing, as in the animation below, f, followed by o to limit the list to windows containing the string "foo".

The animation below illustrates that.

To close a highlighted window, press Shift+Delete.

Ubuntu, including 18.04, is now based on GNOME and some additional features could be made available via GNOME Shell Extensions. Go to the website and search: use "window switcher" as keywords and the relevant extension may be listed in the first page of search result.

This one seems relevant and maintained:

Switcher by dlandau

Switch windows or launch applications quickly by typing

Use the configured global hotkey (Super+w by default) to open a list
of current windows. Type a part of the name or title of the
application window you want to activate and hit enter or click on the
item you wish to activate. You can use the arrow keys to navigate
among the filtered selection and type several space separated search
terms to filter further. Use Esc or click anywhere outside the
switcher to cancel.

Use the configured global hotkey (Super+x by default) to open the
application launcher. Type a part of the name of the application you
want to launch and hit enter. You can use Ctrl+Space or Ctrl+Tab to
switch between the switcher and the launcher, or when there are no
open windows matching a name but there are apps the mode is switched
automatically.

You can customize the look and feel and functionality in the
preferences.

Extension Homepage: https://github.com/daniellandau/switcher

Shell version: 3.30 3.28 3.26 3.24 3.22 3.20 3.18 3.16.3 3.16 3.14

To bind the common keyboard shortcut Alt+Tab or Super+Tab with this extension, user may be required to use a workaround. A GitHub user, PHLAK, has submitted this issue #63 on GitHub and also explained the workaround in several comments:

I would like to bind the Switcher to Super + Tab but am unable to. I've also noticed I cannot bind it to Alt + Tab either.

---

I was able to work around this by setting the value directly with dconf:

dconf write /org/gnome/shell/extensions/switcher/show-switcher "['<Super>tab']"

You can also do the same by using the dconf-config GUI.

---

You might also have to unbind any pre-configured shortcuts using that key combination. Specifically, "Switch applications" is bound to Super+Tab in Gnome.

You can change this by opening the Settings and navigating to Devices > Keyboard. Then Search for Super+Tab and change or remove this binding.

Disclaimer: I do not use Ubuntu 18.04 or GNOME Shell, so I did not test this extension. I merely quoted the most seemingly reliable resources found on the web. The screenshot was redone and optimized (122kB) in GIMP instead, because the original screenshot and the animated image were too large (500kB, 7MB).

TL;DR Go to the GNOME Shell Extensions website and install the extension of choice: Switcher by dlandau. Subject to compatibility with the Shell version.

I think you are specifically looking for "Cycling through windows in a list" feature that is available in Window Manager Tweaks->Cycling in XFCE.

ALT-TAB Cycling in a List

Just for fun

A late home-cooked one:

In action

The setup exists of two tiny scripts, to be saved into one and the same directory:

script 1

#!/usr/bin/env python3

import gi

gi.require_version("Gtk", "3.0")

gi.require_version('Wnck', '3.0')

from gi.repository import Gtk, Wnck, Gdk

import subprocess



css_data = """

.activestyle {

  background-color: grey;

  color: white;

  border-width: 1px;

  border-radius: 0px;

  border-color: white;

}

.defaultstyle {

  border-width: 0px;

  color: black;

  background-color: white;

}

"""



class AltTabStuff(Gtk.Window):

    def __init__(self):

        # css

        self.provider = Gtk.CssProvider.new()

        self.provider.load_from_data(css_data.encode())       

        Gtk.Window.__init__(

            self, title="AltTab replacement"

        )

        self.curr_index = 0

        self.connect('key-press-event', self.get_key)

        self.set_position(Gtk.WindowPosition.CENTER_ALWAYS)

        self.set_decorated(False)

        buttongrid = Gtk.Grid()

        self.add(buttongrid)

        self.connect("delete_event", Gtk.main_quit)



        wins = get_winlist()

        self.buttonindex = 0

        self.buttonsets = []

        index = 0

        for w in wins:

            button = Gtk.Button("t" + w.get_name())

            button.set_relief(Gtk.ReliefStyle.NONE)

            buttongrid.attach(button, 0, index, 1, 1)

            index = index + 1

            button.connect("clicked", raise_window, w)

            self.buttonsets.append([button, w])

        self.set_focus()

        self.show_all()

        Gtk.main()



    def set_focus(self):

        for b in self.buttonsets:

            button = b[0]

            self.set_style(button, active=False)

        newactive = self.buttonsets[self.buttonindex][0]

        self.set_style(newactive, active=True)

        n_buttons = len(self.buttonsets)

        self.buttonindex = self.buttonindex + 1

        if self.buttonindex >= n_buttons:

            self.buttonindex = 0



    def set_style(self, button, active):

        st_cont = button.get_style_context()

        if active:

            st_cont.add_class("activestyle")

            st_cont.remove_class("defaultstyle")

        else:

            st_cont.remove_class("activestyle")

            st_cont.add_class("defaultstyle")

        Gtk.StyleContext.add_provider(

            st_cont,

            self.provider,

            Gtk.STYLE_PROVIDER_PRIORITY_APPLICATION,

        )



    def get_key(self, val1, val2):

        keyname = Gdk.keyval_name(val2.keyval)

        if keyname == "Tab":

            self.set_focus()

        elif keyname == "Alt_L":

            window = self.buttonsets[self.buttonindex-1][1]

            button = self.buttonsets[self.buttonindex-1][0]

            raise_window(button, window)

        elif keyname == "Escape":

            Gtk.main_quit()





def raise_window(button, window):

    subprocess.Popen(["wmctrl", "-ia", str(window.get_xid())])

    Gtk.main_quit()



def check_windowtype(window):

    try:

        return "WNCK_WINDOW_NORMAL" in str(

            window.get_window_type()

        )

    except AttributeError:

        pass



def get_winlist(scr=None):

    """



    """

    if not scr:

        scr = Wnck.Screen.get_default()

        scr.force_update()

    windows = [w for w in scr.get_windows() if check_windowtype(w)]

    return windows





AltTabStuff()

script 2

#!/bin/bash



dr=`dirname $0`

f=$dr'/alttab_runner'



if ! pgrep -f $f

then

$f

else

echo "runs"

fi

Set up

1. 
   

   Not sure if Wnck and/or wmctrl is installed by default, if not:

   
   
   

   sudo apt install python3-gi gir1.2-wnck-3.0
   
   

   
   
   

   and possibly:

   
   
   

   sudo apt install wmctrl
   
   

   
   



2. Save script 1 into an empty file as (exactly) alttab_runner, script 2 as (exactly) alttab_alternative. make both scripts executable



3. 
   

   Disable the existing Alt-Tab:

   
   
   

   gsettings set org.gnome.desktop.wm.keybindings switch-applications '[]'
   
   

   
   


4. 
   

   Set the shortcut (exactly) Alt-Tab to run script 2:

   
   
   

   /path/to/alttab_alternative
   
   

   
   

Usage

Press Alt + Tab to call the switcher (as in the picture), release Alt and press Tab to cycle through the windows, press Alt again to pick the selected window from the list.

Escape will dismiss (close) the switcher.

Options

If you'd like different colors, you can play with the css in script 1 to set your own styling.

To do so, edit this section, where activestyle is obviously the currently selected item:

css_data = """

.activestyle {

  background-color: blue;

  color: white;

  border-width: 1px;

  border-radius: 0px;

  border-color: white;

}

.defaultstyle {

  border-width: 0px;

  color: black;

  background-color: white;

}

"""

See for Gtk css options here on font and buttons.