regina-gui [ file ... ]
Regina is a software package for studying 3-manifold triangulations and normal surfaces. Other key features include angle structures, census enumeration, combinatorial recognition of triangulations, and high-level tasks such as 3-sphere recognition and connected sum decomposition. Regina comes with a full graphical user interface, and also offers Python bindings and a low-level C++ programming interface.
This starts the full graphical user interface, and is the usual way of starting Regina. Any files passed on the command-line will be opened on startup.
If you downloaded a drag-and-drop app bundle, this is the program that runs when you open it. The executable itself is simply called Regina, not regina-gui.
Many people have been involved in the development of Regina; see the users' handbook for a full list of credits.