LibreOffice - Math - Math, LibreOffice, math editor, ODF, OpenFormula, open standards
draw.io - Online diagramming application
Math Magic - MathMagic Equation Editor for Desktop Publishing software & Word Processors, Adobe InDesign, QuarkXPress, MS Word, iWork, for Technical writing with very easy interface and fast input.
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.
KLatexFormula - KLatexFormula is an easy-to-use graphical application for generating images (that you can drag and...
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.