Now that the Android 5.0 docs are available, we have the official documentation for the Toolbar widget:
A standard toolbar for use within application content.
A Toolbar is a generalization of action bars for use within
application layouts. While an action bar is traditionally part of an
Activity's opaque window decor controlled by the framework, a Toolbar
may be placed at any arbitrary level of nesting within a view
hierarchy.
A Toolbar
widget can also be used to replace the action bar:
An application may choose to designate a Toolbar as the action bar for
an Activity using the setActionBar()
method.
The deprecation of tabs in the action bar is most probably due to this, since toolbars cannot contain tab themselves.
Also, it's available for previous Android verions via the appcompat library. See this post by Chris Banes for more information. An excerpt:
Android 5.0 introduces a new Toolbar widget. This is a generalization
of the ActionBar pattern but gives you much more control and
flexibility in using it. Toolbar is a view in your hierarchy just like
any other, making it easier to interleave with the rest of your views,
animate, react to scroll events.