SketchUp - 3D for Everyone
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.
SolidWorks eDrawings - SolidWorks offers complete 3D software tools that are easy to learn and use, and work together to help you design products better.
draw.io - Online diagramming application
PTC Creo Sketch - Creo Sketch is an easy to use 2D CAD application for capturing and creating new 2D freehand concepts which is available on PCs, Macs, and iPads.
Visio - Simplify and communicate complex information using data-linked diagrams.