Run a different window manager in a specific workspace in XMonad

This failed. XMonad works as expected, but applications do not receive pressed keys. I mean, I use winkey as modKey on 5th workspace, and altkey on other workspaces. I used to switch workspaces with modKey+number. When I press Alt+2 on 5th workspace, XMonad does nothing (which is correct), and application does nothing (which is wrong). Chrome does not switch to 2nd tab, and so on.

Okay, so I managed to do it, using XMonad.Actions.PerWorkspaceKeys.

Related configuration:

import XMonad.Actions.PerWorkspaceKeys

workspaceModkeys = [ (mod1Mask, map show ([1..4] ++ [6..9])) -- use Alt as modkey on all workspaces
                   , (mod4Mask, ["5"])                       -- save 5th (use Win there)
                   ]

modifiedKeysList conf =
  [ ((0,         xK_Return), spawn $ XMonad.terminal conf)  -- launch a terminal
  , ((shiftMask, xK_c     ), kill)  -- close focused window
  ]

unmodifiedKeys conf =
  [ ((0, xF86XK_AudioPlay ), spawn "mpc toggle")
  , ((0, xF86XK_AudioStop ), spawn "mpc stop")
  ]

keysList conf = concat (map modifyKey (modifiedKeysList conf)) ++ (unmodifiedKeys conf)

modifyKey :: ((KeyMask, KeySym), X()) -> [((KeyMask, KeySym), X())]
modifyKey k = map (f k) workspaceModkeys
  where
    f ((mask, key), action) (mod, workspaces) = ((mask .|. mod, key), bindOn (map (\w -> (w, action)) workspaces))

myKeys conf = M.fromList $ keysList conf

main = xmonad $ defaultConfig {
  keys = myKeys
}

List modifiedKeys will use modifier (in this example — Winkey on 5th workspace, and left Alt on all others), list unmodifiedKeys is used as is.

Still might look into window-specific keys later, but I'm done for now.

Notice: this answer is based on my understanding of traditional X11. It is possible that this has changed with the introduction of compositing, in which case the following is wrong, but I believe it's still correct.

No, it's not possible to record what's happening on an inactive workspace.

When a workspace is "nonactive" (not shown), the windows it contains are all unmapped. The applications aren't getting expose events and therefore they aren't actually drawing anything (If an application draws a tree in a forest that isn't displayed anywhere, does the tree really exist?).

For your use case, I recommend that you run the application inside an Xvnc server and record that. Example with auto-started session:

# Launch VNC server
vncserver -geometry 1024x768 :10

# Launch a viewer so you can see what you're doing in there
xvncviewer :10

Raw example (start Xvnc directly, no security on VNC connections):

# Start VNC server
Xvnc -geometry 1024x768 :10 &

# Launch a viewer so you can see what you're doing in there
xvncviewer :10 &

# Set your display to the VNC server
DISPLAY=:10

# Launch the desired application in there as well as the recorder
xterm &    # whatever your application is
xmonad &   # if you want a window manager
my-screen-recorder &