plone.app.toolbar installs a new toolbar for Plone. For the moment, it is an experiment only, but hopefully one that will point the way towards Plone's future.
You can use the following buildout to test plone.app.toolbar against Plone 4.2a2 - update versions as applicable:
[buildout] parts = instance extends = http://good-py.appspot.com/release/plone.app.toolbar/1.0a1?plone=4.2a2 [instance] recipe = plone.recipe.zope2instance user = admin:admin eggs = Plone plone.app.toolbar
Make sure you install the "Plone Toolbar" profile when creating your Plone site.