DevLoft in V6. DevSrf is a Lab plug-in for V5.
Users should be aware that in many (most?) cases DevLoft will return a surface which is not exactly developable everywhere. The reason is it creates a surface which runs the full extent of the selected rails, including portions of each rail for which there is not a corresponding part which results in a surface without twist. DevSrf in V5 did not cover the full length of each rail, only the areas which would result in a surface with sufficiently small twist.