Library with extensions for Xfce

 libexo is a library for Xfce that contains a bunch of additional widgets and
 a framework for editable toolbars (an improved version of the framework
 present in GNOME), light-weight session management support, functions to
 automatically synchronize object properties (based on GObject Binding
 Properties) and several miscellaneous utility and helper functions for
 application developers.
 .
 While Xfce ships with quite a few libraries that are primarily targeted at
 desktop development, libexo is targeted at application development, with a
 focus on applications for Xfce.