Houdini is probably the app to look at, as an example, what to implement for a node graph editor. They've been around the longest. TouchDesigner is btw a fork of Houdini. It's long enough ago they may also have added some novel ideas but I wouldn't know.
You can download and play arround with Houdini for free (Apprentice version).
Stuff of the top of my head:
(Grid) snapping
Comments
Underlying nodes with a named, colored rectangle (that stays)
Layouts
Adding vertices to connections to make stuff clearer/disentangle
Coloring nodes/vertices/edges of a graph
Changing node shapes
I suggest watching this video for some inspiration.
Houdini is probably the app to look at, as an example, what to implement for a node graph editor. They've been around the longest. TouchDesigner is btw a fork of Houdini. It's long enough ago they may also have added some novel ideas but I wouldn't know.
You can download and play arround with Houdini for free (Apprentice version).
Stuff of the top of my head:
I suggest watching this video for some inspiration.