From the Windows98SE taskbar it is possible to cascade or tile (vertically
or horizontally) the non-minimized primary windows. The three commands
appear on the right-click menu of the taskbar, which can be hard to target
with a full taskbar.

OS/2 also allowed tiling and cascading, but it was more easily and more
generally afforded. Pressing Button2 on the desktop, or Ctrl+Esc from
anywhere, would present a window with a list of the other windows.
This window was modal; it was either focused or hidden, like a menu.
Windows could be selected from the list and by either a right-click menu
or buttons (in later versions) they could be shown, minimized, maximized,
tiled, cascaded, etc. as a group.

This bug report is filed against the EWMH specification component so
external clients can provide these functions. I mentioned this in
a message to wm-spec-list:
  http://mail.gnome.org/archives/wm-spec-list/2002-May/msg00000.html

Some other functions which people have requested, and some available now
could be provided by such a list. Directional maximize, space filling,
and who knows what else could be provided. A list with grouping by
workspace and DnD would be a way to allow moving windows between
workspaces; so the system menu could be smaller.

IMO, tiling does not need to be exact. A little overlap when tiled
clients are not resizeable by pixel (e.g., terminals) is acceptable.