Heh I recently started developing .NET library with editor for system of in-game NPC dialogues. I would offer you that, unfortunatelly:
1. The editor is WIP.
2. The library itself, even though seems like finished now, may undergo some changes during the works over editor.
3. After Im finished with all of that, then I'm going to actually prepare documentation with some manual.
4. It all takes time, and my life currently, welp.
https://www.youtube.com/watch?v=_burUoFygtI - so few months will pass unfortunately before I will have satisfactory code and programs ready.
5. I'm using .NET2.0 Binary Serialization, so without editor you have no way of creating dialogue files.
6. If you want to use some features (dialogue actions, i.e. passing items during dialogue, and alternative dialogue nodes based on condition, i.e. character doesn't have an item, or story event is yet to happen) you have to change your game code to fit few things it requires to work.
7. Speaking of dialogue actions, I'm still yet to plan the architecture of classes for them, even though I'll probably end up with similar structure as I have for conditions now.
I can provide you with my older version of both library and editor, though
1) DLLs required won't work with Unity - tried it, that was my mistake, thus now creating new, refreshed and slightly more badass version
2) No dialogue actions nor conditions are present
3) I was coding it entirely during my period of my clinical depression recurrence - it's quite a bloody mess.