draw.io - Online diagramming application
UpNote - A beautiful and clean cross-platform app for notes organizer
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.
Notesnook - Notesnook is a simple and private note taking app that keeps your notes organized and synced on your phone, tablet and computer.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
Note Board - Productivity app. Save information like a sticky notes.