Xtpanel builds interactive panels - containing objects such as buttons, sliders, and dialog boxes - from a simple script file or from the command line. With xtpanel, one can quickly add a layer of interactivity to existing software. For instance, a velocity analysis tool can be created in minutes by using xtpanel to add an interactive front end, where sliders choose velocities from a user-specified range, to an existing NMO correction program. Panels can take advantage not only of existing application programs, but also the utilities built into the UNIX operating system. In one example, we use an 80-line script to build an X windows calculator by making a front end to the line-oriented UNIX calculator bc. Another utility built with xtpanel is the xtpanel generator. This is a series of panels that let users build new panels interactively, without having to learn and use the script language.