AngelNode is an open-source visual novel editor designed for the game Angel Wings that's currently in development. You can visit the game's steam page here. It only runs on Windows as it uses WPF and no cross-platform version is currently planned.
The editor is similar to other node-based editors available, offering both a drag&drop UI and a text parsing function for processing larger pieces of script at the time.
Currently there are no project files for the main game publicly released yet, but the editor offers exporting to either the custom Angel Wings .xml based format. Generally any state-machine based visual novel engine should be useable with this editor after making an appropriate building module. Feel free to use this editor for any purpose you want even if it isn't connected to Angel Wings.
Currently no other documentation than the one in code is available, but as the main game will reach release I'll add an XSD Schema and explanation for the .xml format along with a tutorial on how to use this editor.