Gesturefy - Customizable mouse gesture addon, which supports over 40 different actions. Features:
draw.io - Online diagramming application
Easystroke - Easystroke is a gesture-recognition application for X11.
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.
Strokeit - StrokeIt is an advanced mouse gesture recognition engine and command processor.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.