CAT: Content Annotation Tool

CAT, the Content Annotation Tool (formerly known as CELCT Annotation Tool), is a general-purpose web-based text annotation tool.
The aim of the tool is to make the annotation activity as intuitive as possible, supplying, at the same time, a rich set of features. The main strengths of CAT are flexibility, usability and customizability. It also supports multi-layer annotation in order to combine the annotation of several linguistic/semantic levels. It provides a standardized XML stand-off output format to help convertibility, and it contains useful features for searching in files and for measuring inter-annotator agreement between two or more annotators.
CAT is freely available for research purposes.

Reference:

• Bartalesi Lenzi, V, Moretti, G, Sprugnoli, R, 2012 "CAT: the CELCT Annotation Tool". In Proceedings of LREC 2012, Istanbul. (.pdf)