draw.io - Online diagramming application
Synology Note Station - Without needing to spend money on Evernote, Synology Note Station provides a desktop client to organize all your random notes in one place.
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.
Pocket Lists - World’s Friendliest To-Do List App
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
UpNote - A beautiful and clean cross-platform app for notes organizer