Use this tag for questions seeking recommendations which have a graphical user interface and where a command-line answer would be obvious but does not satisfy your needs.
GUI is an abbreviation for Graphical User Interface, a type of user interface that allows users to interact with electronic devices through graphical icons and visual indicators such as secondary notation, as opposed to text-based interfaces, typed command labels or text navigation. (Wikipedia).
In many cases, applications are designed modular, so one can keep the "backend" (e.g. data storage, calculation) and replace the "frontend" (GUI/CLI).