Zenity - Zenity is a tool that allows you to display GTK dialog boxes in commandline and shell scripts.

NirCmd - NirCmd is a small utility that allows you to do many useful tasks from command-line, without displaying any user interface: change your display settings, turn off your monitor, open the door of your CD-ROM drive, and more...

Yad - Yad (yet another dialog) is a fork of Zenity with many improvements, such as custom buttons...

wxFormBuilder - wxWidgets is an excellent framework that enables the creation of multi-platform applications with...

Dialogblocks - DialogBlocks is a cross-platform wxWidgets dialog editor for Windows, Unix and Mac.

xdialog - Xdialog is designed to be a drop in replacement for the "dialog" or "cdialog"...