The geotoolkit.org web site has very little documentation. From this document I get the impression that it is a fork from geotools; is that right? If so, what were the motives/objectives of the fork?
It looks like there was a fork that was intended to be reintegrated, but this never happened.
There is also an interesting mailing list discussion on GeoTookits application to become an OSGeo project (as well as GeoTools), fragmented communities, and various opinions on the divide.
We can't say which is the fork. martin desruisseaux made the referencing, metadata and coverage modules since 1996. geotools suffer a huge contribution dropdown in 2008 when the five developers leaved to make geotoolkit.
Both projects are equaly active. see http://www.ohloh.net/p/compare_chart?metric=Activity&project_1=GeotoolKit&project_0=GeoTools (green : geotoolkit, value is in number of commits)
Geotools just has the name. it's not even following the GeoAPI ogc spec anymore.
unlike geotools (which is nearly only working for geoserver), geotoolkit developers are working on several different type of gis project. - Constellation-SIG : map server - Mapface : JSF map library - MDWeb : metadata catalog - Puzzle-GIS : desktop application on netbeans platform