What it is:
Fast Light Toolkit – user interface designer. This package provides
Fluid, an interactive GUI designer for FLTK, allowing graphical
development of FLTK-based user interfaces. It natively works with
(textual) .fl files, but also includes rough support for reading .fd
files produced by fdesign (in libforms-bin).
The Fast Light Toolkit (FLTK) is a cross-platform graphical user
interface toolkit originally based on libForms.
To know more about:
To install in Ubuntu:
sudo apt-get install fluid