Pollen is a publishing system that helps authors create beautiful and functional web-based books. Pollen is a package of tools for writing, designing, programming, testing, and publishing.
I used Pollen to make my book @link["http://practicaltypography.com"]{Butterick's Practical Typography}. If that looks better than the last digital book you encountered, read on.
Pollen is built around two ideas. First, that digital books should be the best books we've ever had. (So far, they're not even close.) Second, that if digital books are software, an author shouldn't think of their book as merely data. The book is a program.
Not that you need to be a programmer to use Pollen. On the contrary, the Pollen language is markup-based, so you can write & edit text naturally. But when you want to automate repetitive tasks, add cross-references, or pull in data from other sources, you can access a full programming language from within the text.
That language is Racket. I chose Racket because while the idea for Pollen had been with me for several years, it simply wasn't possible to build it with other languages. So if it's unfamiliar to you, don't panic. It was unfamiliar to me. Once you see what you can do with Pollen & Racket, you may be persuaded. I was.
If the file extension is ``@(format ".~a" world:preproc-source-ext)'', the source is interpreted as @racket[pollen/pre] (``pre'' stands for ``preprocessor'').