[zdw]

If you want to integrate both text and freeform diagramming, the diagrams.net tool will support embedding Mermaid:

https://www.diagrams.net/blog/mermaid-diagrams

They're not editable afterward, but it sometimes comes in handy if you want to render them out as an image for a document/presentation.

[alixanderwang]

Terrastruct offers this too, with the bonus that the freeform changes get saved to the text: https://youtu.be/EhxVVkxv2Ns?t=128

(it is a paid product though, whereas diagrams.net is free)

[flanked-evergl]

Diagrams.net also supports plantuml and you can edit them afterwards.