How cycle through applications in Xubuntu without using Alt-Tab?

That seems to be what "Switch application" does in Xfce.

Go to Settings > Window Manager and select Keyboard tab. In the left column "Action", look for "Switch application". Select the row, then either press Enter key or double-click on mouse. A small window will appear, ready to accept key press and register a new shortcut.

The action has no shortcut, therefore does nothing, by default. When enabled, the action will switch applications immediately from one to another.

The behaviour of "Switch application":

• Unlike "Cycle windows" or Alt+Tab, the popup window will not be displayed.

• The action does not switch to all currently running programs.

• For example, the action can not switch to Settings Manager but can switch to Application Finder in Xfce 4.10 (14.04) and newer. The result is reversed in older system i.e. Xfce 4.8 (12.04).

• From my observation, the action will switch from oldest running program to newest running program and repeat the loop. The switching order is likely non-customizable.

Not all programs are applications. Some program has different type of window (dialog) compared to other programs (normal). The window type can be checked by using xwininfo -wm command.

Enable "Switch application" and try it for yourself.