Zenity - Zenity is a tool that allows you to display GTK dialog boxes in commandline and shell scripts.
wxWidgets - wxWidgets: Cross-Platform GUI Library
Yad - Yad (yet another dialog) is a fork of Zenity with many improvements, such as custom buttons...
Electron - Build cross platform desktop apps with web technologies
Glade - Glade is a RAD tool to enable quick & easy development of user interfaces for the GTK+ toolkit...
GTK - GTK+ is a multi-platform toolkit for creating graphical user interfaces.