OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.
SciDaVis - SciDAVis is a free application for Scientific Data Analysis and Visualization.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
DPlot - DPlot graphing software lets scientists and engineers graph, plot, analyze, and manipulate data.
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.
WinPython - The easiest way to run Python, Spyder with SciPy and friends out of the box on any Windows PC...