CodeShare.io - Realtime code sharing for developers
draw.io - Online diagramming application
Code2Flow - An easy solution to create product flows.
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.
Code.gov - Share & reuse open source code from the Federal Government
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.