iA Writer has just become version 4! It coms with some really impressive features, that definitely makes it more than just a basic text editor.
There's better way to add images (with support for better captions), stress free tables with .csv file embeds, embedded text files, and all of these "content blocks" can be chained together! Which means you can have a book outline document, with references to the title page, individual chapters, etc. But within those chapters you could have references to images, or maybe even more text! The possibilities are endless, and I'm really impressed.
I was going to write a big article about this update, but I saw on the iA blog they have a super helpful video that explains everything!
Read the full article about iA Writer 4 on the iA Blog.