Leo is some kind of text editor with the ability to aggregate files and parse special processing directives. It can be seen as a tool to create and manage graphs of text fragments. Where Leo shines is for extracting some code fragments, using its own directives. There is some likeliness with Novelang, that has books including parts. I don't want anything like a graphical front-end for Novelang now but there may be some ideas to steal from Leo.