GeoTools 2.6.6 was created on March 19th, 2010:

This release contains a number of minor bug fixes and improvements, and marks the end of the 2.6.x series.
The stable development continues on the 2.7.x series, which is about to be released as 2.7.0 final.
This release is made in conjunction with GeoServer 2.0.3.

For more information please review the Release Notes:

For more information on GeoTools and the 2.6 series: