RealTerm - RealTerm is a terminal program specially designed for capturing, controlling and debugging binary...
draw.io - Online diagramming application
Tera Term - Tera Term (Pro) is a free software terminal emulator (communication program) for MS-Windows.
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.
HTerm - HTerm is a terminal emulator for serial communication.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.