A side effect of changes in NetBeans Platform 7.1 in the NetBeans window system is that palettes can now be created for view TopComponents.
Below, a TopComponent in the "explorer" position is selected, which results in the Palette opening and showing items that can be dragged into the TopComponent:
And here, in the same application, a TopComponent in the "output" position is now selected, which causes the Palette to open, showing items that are relevant to the TopComponent:
I copied code used in the above two TopComponents from this blog entry:
Related issue: http://netbeans.org/bugzilla/show_bug.cgi?id=209238