I'm the developer of Highlight Vault, a Windows desktop tool that pulls your book highlights out of Kindle's My Clippings.txt, a Kobo device, or a CSV/JSON import, and organizes them into one searchable local library — nothing leaves your computer, no account required.
Free tier:
Kindle and Kobo highlight sync, plus CSV/JSON import
Browse & Search across every highlight and note, with genre/colour/date filters
Favorites and manual collections
Export to Word, CSV, or JSON
Pro tier (one-time purchase, no subscription) adds scheduled autosync, Notion/Obsidian/Google Docs push, EPUB/PDF/Anki export, a stats dashboard, keyword theme clustering, a highlight timeline, spaced-repetition review, smart collections, bulk actions, per-highlight tags, custom colour labels, and — new as of this week — a read-only Calibre library integration that pulls in series info, tags, and cover art for matching books without ever touching your Calibre library.
Free:
https://highlightvaultapp.gumroad.com/l/nxaife
Pro:
https://highlightvaultapp.gumroad.com/l/sjnjbm
Windows 10/11, no Python or technical setup needed. Happy to answer questions about how it handles [whatever's relevant — Kobo, Calibre, Goodreads, etc.].