Or, less ergonomically, the general rectangle-editing commands built into more powerful code editors e.g. Emacs.
With these, simple but fairly pretty box+line+text diagrams can be inlined with your source code comments. This unification may help in the perennial struggle to keep software architecture and source code reality in sync.
(ascii to diagram)
Typogram https://code.sgo.to/typograms/#installation
Markdeep https://casual-effects.com/markdeep/
svg bob editors https://ivanceras.github.io/bob-editor/ https://mbarkhau.github.io/asciigrid/
Ditaa https://ditaa.sourceforge.net/
Goat https://github.com/blampe/goat
Protocol https://www.luismg.com/protocol/
(dsl to ascii)
https://diagon.arthursonzogni.com/#Sequence
https://textart.io/sequence
https://weidagang.github.io/text-diagram/
https://diagwiz.io/playground/