Color Palette Generator - Enter the URL of an image and find its color palette
draw.io - Online diagramming application
Color Hunt - Curated collection of beautiful colors, updated daily
Dia - Dia is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license.
Coolors.co - The super fast color schemes generator! Create, save and share perfect palettes in seconds!
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.