There are literally hundreds of smaller developers (I.e. OpiText) who have tried to enter this industry, but, to my knowledge; they haven't been very successful. The big business software developers haven't jumped on this audience, simply because there is a very little market for this kind of software.
It is extremely challenging for software developers to provide non tech-savvy artists (fashion designers) with a software solution that can provide them with the desired level of flexibility and creative freedom. Most designers probably stick to pen and paper; they simply don't want to spend their time on software.
The few designers who go digital probably use software like Adobe Photoshop, Corel Painter or ArtRange, where they can express themselves freely, by free-hand painting with a Wacom tablet. That, or they'll just get a good scanner to digitize their designs.
The more tech-savvy designers might use 3D modelling software. Although not specifically developed for fashion designers, AutoDesk's 3D Studio Max or Maya, Luxology's Modo, Rhino etc. can provide a great deal of flexibility and creative freedom, but the learning curve can be rather steep.