OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.

GnuPlot - Gnuplot is a portable command-line driven interactive data and function plotting utility.

PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.

Dr. Geo - Dr. Geo, a software to design & manipulate interactive geometric sketches.

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.

Giac/Xcas - Free computer algebra system