The Professional GUI was released in the 3.3 series of Smallworld. It was GE's first attempt at having the user interface more MS Windows-like. It was short lived and replaced by the Smallworld Application Framework (SWAF) in the 4.X releases. The concepts may be similar between 3.3 and 4.X (like the use of XML configurations) but there are many differences on implementation.
This is the classic "UNIX" look still used by the CASE tool. To me it was the simplist GUI to develop in, but had underlying issues with GUI component communications. This was the standard interface prior to 3.3. It is still supported for use on UNIX based systems. Although I understand the SWAF interface could be available on UNIX if there was enough demand.. Could we hope for a Mac OS option one day??