The ATK library provides a set of interfaces for accessibility.
By supporting the ATK interfaces, an application or toolkit can
be used with such tools as screen readers, magnifiers,
and alternative input devices.

Atk provides a core set of interfaces which are common to all
widgets and "additional" interfaces that are appropriate to certain
classes of widgets and whose existence can be queried at run time.
It also provides interfaces which an application can use to provide
additional accessibility information to assistive technology tools.

Homepage:
http://developer.gnome.org/atk/
