The computer programs most users interact with daily are driven by a graphical user interface (GUI). However, many scientific applications are used with a command line interface (CLI) for the ease of development and increased flexibility this mode provides. Scientific application developers would benefit from being able to provide a GUI easily for their CLI programs, thus retaining the advantages of both modes of interaction. GuiLiner is a generic, extensible and flexible front-end designed to ``host'' a wide variety of data analysis or simulation programs. Scientific application developers who produce a correctly formatted XML file describing their program's options and some of its documentation can immediately use GuiLiner to produce a carefully implemented GUI for their analysis or simulation programs.