AGTK is a suite of software components for building tools for annotating linguistic signals, time-series data which documents any kind of linguistic behavior (e.g. audio, video). The internal data structures are based on annotation graphs. Annotation Graphs are a formal framework for representing linguistic annotations of time series data.

(Note: last release 2007. Last update on sourceforge page 2011). The links on the sourceforge page are broken: software is reportedly released under a 'Common Public Licence', although the link to the licence at http://www.opensource.org/ is broken; link to the project website at the Linguistic Data Consortium is broken.