If you're looking for suggestions: If you really want people to use this as a writing tool, make the interface itself more tranquil - the "Tranquillity" title is distracting, and the poem title typeface is awful. Not everyone who writes poetry is into that kind of frilly aesthetic. Find a few well-designed poetry books to use as design examples. A full-screen mode would be easy to implement and super useful.

Similarly, the rhyming tools are interesting, but make them hideable for anyone who is not using them. I would use a thesaurus a thousand times more often than a rhyming dictionary.

I actually like the fixed-width font but suspect many wouldn't. Maybe an option to switch between fixed-width and not. Also, I expect to be able to use the tab key to indent, but it doesn't work here.

Saving and revision control would be great.