Install fluid by entering the following commands in the terminal:
sudo apt update sudo apt install fluid
Description:
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.
Homepage: http://www.fltk.org/
Version: 1.3.4-6
Section: universe/devel