I haven't found an addon yet to do this. Basically. I have and I am sure many other do also, many chat windows with specific information sent to them. For me, I have a whispers window, Nurfed combat log window, General Chat window (general, trade, guild, officer, etc..) a window that just shows dmg i take and nothing else, a Nurfed COmbat log of dmg our MT(s) take during raiding and finally, a window for loots.
As it stands, the only window you can dock other windows on is the General Chat window. I have 3 windows docked there, but would prefer if I can dock windows together on any window I decide.