The gml4gtk 7.2 version is supposed to have html label support with <table> data.
The support page for gml4gtk is at https://graphviewer.nl/
The blog documents more graph layout issues and screenshots and newest developments at https://myogdf.blogspot.com/
One of the issues to fix is incremental graph layout for the cluster subgraphs and more graphviz language support.
On graphviewer.nl is also online graph layout and here are more online sites for diagram drawing or graph layout and some are free software to run on own webserver
Markdeep https://casual-effects.com/markdeep/
markdown, ascii-to-all
Svgbob https://ivanceras.github.io/svgbob-editor/
ascii-to-all
Archetype https://fatiherikli.github.io/archetype/
ascii-drawing
Textik https://textik.com/
ascii-drawing
ASCIIFlow http://asciiflow.com/
ascii-drawing
Pikchr https://pikchr.org/home/pikchrshow
all
Kroki https://kroki.io/
BlockDiag, SeqDiag, ActDiag, NwDiag, PacketDiag, RackDiag, BPMN, Bytefield, PlantUML, Ditaa, Erd, Excalidraw, GraphViz, Mermaid, Nomnoml, PlantUML, SvgBob, UMLet, Vega, Vega-Lite, WaveDrom
BPMN Sketch Miner https://www.bpmn-sketch-miner.ai/
BPMN/flow
Webgraphviz http://www.webgraphviz.com/
graphviz
Viz.js http://viz-js.com/
graphviz
Edotor https://edotor.net/
graphviz
nomnoml http://www.nomnoml.com/
activity, class
Source: https://github.com/skanaar/nomnoml
CodeUML http://codeuml.com/ (dead)
uml
Source: https://github.com/oazabir/codeuml
yuml https://yuml.me/diagram/scruffy/class/draw
uml
PlantText http://www.planttext.com/planttext
activity, class, component, object, use case, state, graphviz, sequence, gui, earth
PlantUML http://www.plantuml.com/plantuml/uml/
activity, class, component, object, use-case, sequence, state, deployment, timing, gui, archimate, gantt, mindmap, tree, math, entity-relationship
Umple Online http://cruise.site.uottawa.ca/umpleonline/
class, state, composite
ZenUML https://app.zenuml.com/
sequence
DotUML https://dotuml.com/playground.html
class, use case, sequence, state, deployment, graphviz
QuickDBD https://app.quickdatabasediagrams.com/#/
entity-relationship
dbdiagram https://dbdiagram.io/d
entity-relationship
WebSequenceDiagrams https://www.websequencediagrams.com/
sequence
SVG Sequence Diagram http://sullerandras.github.io/SVG-Sequence-Diagram/
sequence
JUMLY http://jumly.tmtk.net (dead)
sequence
Source: https://github.com/tmtk75/jumly
js sequence diagrams http://bramp.github.io/js-sequence-diagrams/
sequence
swimlanes https://swimlanes.io/
sequence
SequenceDiagram https://sequencediagram.org/
sequence
GraphUp https://graphup.co/ (broken)
sequence, gantt
Text Diagram http://weidagang.github.io/text-diagram/
ascii sequence
Source: https://github.com/weidagang/text-diagram
ASCII Sequence Diagram Creator https://textart.io/sequence
ascii sequence
Chart Mage http://chartmage.com/index.html
sequence, flow
flowchart.js http://flowchart.js.org/
flow
drawthe http://go.drawthe.net/
network
Source: https://github.com/cidrblock/drawthe.net
mermaid https://mermaid-js.github.io/mermaid-live-editor/
flow, sequence, class, state, entity-relationship, gantt, pie, journey
Diagram.codes https://www.diagram.codes/
flow, sequence, graph, tree, onion, stack, system, timeline, mindmap
Blockdiag http://interactive.blockdiag.com/
block, activity, network, rack/stack, packet
state machine cat https://state-machine-cat.js.org/
state
Source: https://github.com/sverweij/state-machine-cat
MetaUML https://metauml.denksoft.com (dead)
Railroad Diagram Generator http://www.bottlecaps.de/rr/ui#_StringLiteral
railroad/syntax
Gleek https://www.gleek.io/
architecture
Ilograph https://app.ilograph.com/
architecture
Structurizr https://structurizr.com/dsl
architecture
Penrose https://github.com/penrose/penrose
penrose
code2flow https://app.code2flow.com/
flow
flowchart.fun https://flowchart.fun/
flow
WaveDrom https://wavedrom.com/editor.html
timing
CLI Text to Diagram Tools
perl graph-easy http://bloodgate.com/perl/graph/index.html #cli
flow
Doc: https://developpaper.com/recommend-a-tool-for-making-ascii-flow-chart-graph-easy
Example: graph-easy <<< [node 1]->[some text]-[this][node 1]->[branch]