Mermaid is an open source tool that can be used to create such charts using Markdown plaintext

A split screen view showing on the right a flowchart that starts out with a block saying Brainstrom article, which then points to a small block saying send pitch. On the left side is seen the plain text code that creates this chart. It shows a line A[Brainstorm article] -->|send pitch| etc and continues on.

Quickly create a flowchart, mindmap, or Gantt chart without once touching your mouse.

Open source means it is not going to suddenly disappear tomorrow, it can be broadly supported across different platforms and Markdown editors, and you can see what it is doing (not a binary storage blob).

Wherever a Markdown editor has support for Mermaid (often through a plugin) this type of chart and diagrams will work. For those who do tables in Markdown, Mermaid’s syntax will look familiar.

Plain text format means it will still be readable in 500 years time when Microsoft is long gone.

The linked article also gives a link to the online Mermaid site where you can test this out, or design your chart and then copy the code to your Markdown file.

See https://lifehacker.com/tech/mermaid-creates-diagrams-and-flowcharts-with-plaintext