Overview
Most ebook readers only display text, audiobook players narrate without context, and highlights fade from memory. Kepler is a native Android app built on one premise: books should be internalized, not just consumed. It unites an EPUB reader, narration with sentence-level read-along and an active recall loop in one place.
Key Features
- Read: EPUB reader on Readium 3.4 with Literata typography, paper themes and SQLite FTS5 in-book search
- Listen: Fish Audio or fully offline system TTS, highlighted sentence by sentence as it plays through a Media3 player with sleep timer and lock-screen controls
- Remember: FSRS-6 flashcards, chapter packs (gist, key ideas, concepts, check-in questions) and a concept map of what you have read
- The AI Fence: every LLM prompt is clipped at your reading position, so recaps, answers and cards never spoil what comes next
- Open Exports: highlights and notes as Obsidian-friendly Markdown with deep links back to each sentence, or W3C Web Annotation JSON
Technical Details
A modular Kotlin codebase (core, engine and feature layers) built with Jetpack Compose and Material 3 Expressive. A "text spine" gives every sentence a deterministic id, so bookmarks, highlights, audio sync and study cards survive re-pagination. No analytics or tracking: bring your own Fish Audio and OpenRouter keys, encrypted at rest with AES-256-GCM in the Android Keystore. Licensed GPL-3.0, with signed releases built by GitHub Actions.