GuiXT is a client-server system that provides user interface customization for SAP solutions. It allows users to integrate images, rearrange fields, and add buttons to SAP forms using a simple scripting language. To create a GuiXT script, a user logs into SAP, activates GuiXT for a screen, and edits the script using the Synactive GuiXT editor or Designer tool. GuiXT comes free with SAP GUI but additional products like Designer, InputAssistant, and Viewer are available for purchase.