What is "Webpub"?
https://www.npmjs.com/package/@nypl/epub-to-webpub
https://www.npmjs.com/package/epub-to-webpub
https://www.npmjs.com/package/library-simplified-webpub-viewer

EPUB Object Model striving to be standards compliant
https://www.npmjs.com/package/epubavocado

Reads and writes OPF & NCX files 
https://www.npmjs.com/package/@mfgames-writing/opf
https://www.npmjs.com/package/@mfgames-writing/ncx

Reads OCF -- VERY OLD -- IGNORE?
https://www.npmjs.com/package/epub-ocf

CSS (SCSS) stuff for ebooks
https://www.npmjs.com/package/buckram

Study
https://www.npmjs.com/package/epub2

EPUB Object for TypeScript
https://www.npmjs.com/package/epub-object-ts

EPUB Metadata Parser
https://www.npmjs.com/package/epub-metadata-parser

Accessibility checker
https://www.npmjs.com/package/@daisy/ace
https://www.npmjs.com/package/@daisy/ace-cli
https://www.npmjs.com/package/@daisy/epub-utils

EPUB Checker
https://www.npmjs.com/package/epubchecker
https://www.npmjs.com/package/epub-check

Word count
https://www.npmjs.com/package/epub-wordcount

Vivliostyle - Typesetting? - Study what this is
https://www.npmjs.com/package/@vivliostyle/core
https://vivliostyle.org/

Convert to KEPUBS for display on Kobo readers
https://www.npmjs.com/package/kepuber

EPUB->AZW3 conversion (Kindle)
https://www.npmjs.com/package/ebook-batch-converter

PDF conversion
https://www.npmjs.com/package/@someok/txt-to

Hyphenate
https://www.npmjs.com/package/epub-hyphen

PostCSS prefixing EPUB properties
https://www.npmjs.com/package/postcss-epub

ACSM?  What's this?  Converts to EPUB
https://www.npmjs.com/package/acsm-to-epub

OPDS?
https://www.npmjs.com/package/opds-extra
https://www.npmjs.com/package/calibre-opds

Converts multipage image-only PDF into EPUB
https://www.npmjs.com/package/synpub-sdk