Koreader on itself is an awesome book reader for Kindle e-ink devices. But plugins make it even better.
- Assistant: AI Helper Plugin
- Filebrowser plugin
- Rakuyomi - Manga reader plugin
- Audiobookshelf Browser
- WebDAV Highlights Exporter
- Hardcover.app Integration
- Crosswords
- Calculator
- Kompanion - Self-hosted library with OPDS server for progress syncing and books downloading
In general you need the dictionaries in StarDict format