Most every chart type are currently used in professional production environments. Though a dev release, it, too, is stable. So, what's version 1.0 waiting on V1.0 will likely have a new interface, which will have a GDChart instance, rather than all those globals. This will allow the header files to finally be cleaned up. V1.0 will have support for TTFs.
Legends are high on the TODO list.
DONE Arrays interface rather than the var args, for calling flexibility and compatibility with other interfaces .