ProProfs Knowledge Base - ProProfs Knowledge Base is a cutting-edge knowledge management software that assists businesses to reduces support tickets by self-help and create online manuals, guides, wikis, documentation, FAQs and more.
draw.io - Online diagramming application
Baklib - Make your knowledge base & help document online
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.
Solina Mind Mapping - Solina Mind Mapping is a smart mind mapping program and editor for capturing, refining, organizing and sharing the ideas with others.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.