draw.io - Online diagramming application
GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
LabPlot - LabPlot is a KDE-application for interactive graphing and analysis of scientific data.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Matplotlib - matplotlib is a python 2D plotting library which produces publication quality figures in a variety...