This is pretty neat.  It's a TabPage control that allows you to drag out your tabs and dock them.  Visual Studio has this feature, but I've never tried to do it on my own.

From the introduction:

Have you ever made a nice stable winForm application that had several tabs?  Did it contain a nice clear distinction of workflow or had just a real nice component separation? Then did you find out some time later (weeks or months) that some of your users want to see some of the data side by side and that they have been flipping back and forth furiously just to see the information? If this describes a situation that you find yourself in and you don't want to go through all the effort of a MDI interface then the PullApartTabPage might be just right.