OmniGraffle - OmniGraffle is for creating precise graphics like website wireframes, an electrical system designs, or mapping out software class.
GeoGebra CAS Calculator - Free online algebra calculator from GeoGebra: solve equations, expand and factor expressions, find derivatives and integrals
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
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.
GeoGebra - GeoGebra is free and multi-platform dynamic mathematics software for learning and teaching.