Until recently (3/4 years ago?) I had been using Window Maker. Since 1998.
My only reason for abandoning it is because it doesn't support workspaces arranged in a matrix, only as an array.
I started using workspaces in a 3x3 grid, with the center one the "main" one and each of the compass points from center dedicated to a specific project.
Maybe I should see if Window Maker can be modified the way I want it to be.
Windowmaker allows you to map keybindings to workspaces, the default is to use the first 12 function keys. That's ... usually ... enough for me.
You can also pin the workspaces menu as a poor man's switch / navigation tool.
Logically, Windowmaker's workspace topology is either a list or a loop (daisy chain), depending on whether or not you've configured it to wrap last to first or not.
Fvwm is maintained. Vtwm is maintained. Ctwm is maintained. Mwm is maintained. Window Maker seems to be maintained. CDE has been resurected. etc.