Workflowy - A better way to organize your mind.
draw.io - Online diagramming application
SuperNotecard - Introducing SuperNotecard. SuperNotecard is an online writing tool that features virtual notecards to help arrange facts or scenes, track details, organize paragraphs, and clarify your composition process.
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.
Dynalist - Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.