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Own your reading data.
Forever.

A fast, local-first reading app for Linux, macOS, Windows, and Android. It opens PDFs, EPUBs, and RSS feeds in under 50ms—and saves every highlight as plain Markdown directly to your Obsidian or Logseq vault.

No accounts, no subscriptions, and zero tracking. Everything runs locally on your machine and stays on your disk.

Zero Telemetry Plain Markdown on Disk Works 100% Offline MIT Licensed
Native Standalone Builds
v1.5.7
Linux One-Liner Install Auto-detects distro
curl -fsSL https://raw.githubusercontent.com/fundaments-work/Theorem/main/scripts/install-linux.sh | bash
All downloads SHA-256 verified · Also available on GitHub Releases
Performance
< 50ms Startup

Native Rust pre-parser inflates 100MB+ books instantly

Storage
Plain Markdown

Notes save directly to your drive with YAML frontmatter

Dictionary
< 1ms Lookups

Memory-mapped StarDict queries 800,000+ words offline

License & Cost
$0 Free (MIT)

Zero subscriptions, no accounts, and zero telemetry

Your Notes on Your Disk

Read on the left. Notes sync to Obsidian on the right.

Every highlight and annotation writes to your drive as plain Markdown. No cloud relay, no export button needed.
| Bertrand_Russell_1917_Mysticism_and_Logic.epub [EPUB 3.2 · 318 pages]
WI-FI SYNC: 2 DEVICES CONNECTED (HOME NETWORK ONLY) | LOCAL FILES ON DISK
Chapter II · Constituents of Matter Page 38 / 294

Metaphysics, or the attempt to conceive the world as a whole by means of thought, has been developed, from the first, by the union and conflict of two very different human impulses: the one urging men towards mysticism, the other urging them towards empirical observation.

The greatest men who have been philosophers have felt the need both of science and of mystical insight: the result has been the creation of a great philosophy. But while the scientific attitude is cautious, tentative, and experimental, the mystical certainty is swift, complete, and profound. A scientific philosophy must seek to eliminate the human element, rather than place man at the apex of the cosmic edifice.

Theorem Footnote Preview [14]
Instant Peek

[14] Cf. Russell, B., Our Knowledge of the External World (1914), Lecture III: “On the Nature of Acquaintance and Epistemological Isolation.” Saved to vault/notes/russell-1914.md.

Dictionary definition available offline Open Note →

To realize the unimportance of time is the gate of philosophical wisdom. In this, mysticism is right; but in its negative attitude towards empirical relation, it leads dialectic into contradiction.

6-COLOR HIGHLIGHTS:
Custom fonts · Dark mode · Fast rendering
sync treatise-russell-1917.md
Obsidian / Logseq Mirror
---
title: Mysticism and Logic
author: Bertrand Russell
year: 1917
folder: notes/philosophy
status: saved_locally
last_export: 2026-09-19T08:45:00Z
---
# Highlights & Notes
## Page 38 (Chapter II)

> Metaphysics has been developed by the union of mysticism and empirical observation.

#thesis #observation (yellow / blue)

> ...the mystical certainty is swift, complete, and profound.

Note: Compare with Wittgenstein Tractatus 6.522.
NOTES IN SYNC ON YOUR HARD DRIVE 100% PLAIN TEXT (.MD)
Interface

See Theorem in Action

A minimal, uncluttered workspace designed for deep focus across desktop, tablet, and mobile screens.

Theorem reader interface with color-coded highlights and dark mode
Reading Workspace

Reflowable Reader & Footnote Portals

Distraction-free EPUB and PDF reading with 6-color highlights, custom typography, and in-place Theorem Lens footnote peek portals.

Theorem library screen with custom shelves and book grid
Library Management

Library, Shelves & Reading Progress

Organize thousands of books into custom shelves. Track reading progress, page counts, ratings, and 12-week reading heatmaps.

Theorem annotations drawer showing color-coded highlights and notes
Highlights & Notes

Color Taxonomy & Annotations Drawer

Quickly browse, filter, and edit all highlights across books and articles. Export quotes or share them as stylized card images.

Theorem RSS feed reader with article view
Web & RSS Feeds

Distraction-Free RSS & Article Feeds

Native Rust readability engine extracts clean text and images, removing ads and tracking cookies with offline SQLite caching.

Theorem offline vocabulary and dictionary lookup workspace
Vocabulary Builder

Offline StarDict Vocabulary Workspace

Instant sub-millisecond word lookups from memory-mapped 800,000-word offline Wiktionary directly on disk.

Theorem running on Android mobile and tablet screens
Android Companion

Android Mobile & Tablet Experience

Native touch reading, annotations, and quick highlight lookup on Android phones and tablets.

Feature Directory

Everything Engineered into Theorem

An exhaustive breakdown of capabilities built for researchers, students, and power readers.

Performance & Formats

Opens in Under 50ms (EPUB, PDF, CBZ & RSS)

Native Rust pre-parser opens 100MB+ books in under 50ms. Reflowable EPUBs, academic PDFs with zoom, manga CBZ/CBR, and distraction-free RSS feeds in one quiet window.

PKM Integration

Automatic Obsidian & Logseq Sync

Every highlight and note is written directly to your vault folder as standard Markdown (.md) with YAML frontmatter, tags, and timestamps. No plugins or cloud relays required.

Academic Reading

Theorem Lens (Footnote & Citation Portals)

Click footnotes, citations, and figure references to preview them in a floating popover portal. Read the citation instantly without losing your reading position.

Offline Dictionaries

Sub-Millisecond StarDict Lookups (< 1ms)

Queries 800,000+ words in under 1ms using memory-mapped dictionaries on disk. Download offline English Wiktionary in one click, or import custom StarDict files.

Immersion Audio

Offline Neural Voice & Audiobook Player

Listen with an offline Supertonic 3 neural voice that synthesizes on your CPU without cloud API calls. Or attach any DRM-free .m4b or .mp3 audiobook with chapter marks.

Local-First Sync

Encrypted LAN Device Sync

Pair your computer, tablet, and Android phone using a simple QR code. Syncs reading progress and notes over your local home Wi-Fi with end-to-end encryption.

Complete Architecture

Engineered for Every Aspect of Reading & Knowledge

An exhaustive catalog of built-in capabilities—zero third-party subscriptions or cloud plugins required.

menu_book

Reading & Document Engine

High-performance reading across books, academic papers, manga, and newsletter feeds.

  • Multi-Format Support

    EPUB, MOBI, AZW, AZW3, FB2, CBZ, CBR, PDF, and RSS feeds in one quiet app.

  • Sub-50ms Book Opening

    Native Rust pre-parser inflates stylesheets and chapters in parallel threads.

  • Streaming In-Book Search

    Multi-threaded search crawls 1,000+ pages in 10–30ms with zero UI lag.

  • Theorem Lens

    In-place popover portal previews footnotes, citations, and figures without flipping pages.

  • Reflowable & Fixed Layouts

    Switch between paged book layout and continuous vertical scrolling anytime.

  • Academic PDF Engine

    PDF.js engine with zoom (50%–200%), page-fit, width-fit, and outline navigation.

  • Session Persistence

    Saves page-accurate CFI progress, zoom, mode, and scroll position per-book.

speed

Speed Reading & Ergonomics

Rapid serial visual presentation, adaptive time estimation, and deep typography controls.

  • RSVP Speed Reading Mode

    Flashes words sequentially at a fixed visual focal point at 300–800+ WPM to eliminate eye fatigue.

  • Adaptive Reading Time Engine

    Rolling EMA WPM engine estimates exact remaining chapter and book reading time based on your real speed.

  • Deep Typography Controls

    Adjust font family (Serif, Sans, Mono), size (12–32pt), line height (1.0–2.2), and hyphenation.

  • Focus Themes & Full-Screen

    Light, Sepia, and Dark themes with customizable brightness, auto-hiding toolbars, and zen full-screen.

edit_note

Annotations & Pen Inking

Capture quotes, thoughts, and sketches directly in context with zero latency.

  • 6-Color Highlight Taxonomy

    Yellow, green, blue, red, orange, and purple highlights to categorize arguments.

  • Drawing Overlayer Styles

    Choose between highlight, underline, strikethrough, squiggly, or outline.

  • Freehand PDF Inking

    Draw diagrams and margin notes directly on PDF pages with pen stroke controls.

  • Context Notes & Bookmarks

    Attach rich text notes to any highlight or place bookmarks for quick reference.

  • Global Annotations Drawer

    Browse, filter, edit, and jump to any annotation across your entire library.

share

Highlight Sharing & Quote Cards

Turn meaningful passages into beautifully typeset cards ready for social feeds and notes.

  • Multi-Format Quote Cards

    Generates high-resolution share cards in Square (1080×1080) and Story (1080×1920) aspect ratios.

  • 4 Visual Card Themes

    Choose from Match Reader Background, Dark Carbon, Tinted, or Warm Sepia card styling.

  • Instant Clipboard & Image Export

    Copy formatted quote images directly to clipboard as PNG, save to disk, or share via native Web Share API.

sync_alt

PKM & Markdown Vault Mirror

Seamless local-first integration with Obsidian, Logseq, and plain text notes.

  • Direct Vault Mirror

    Every highlight and note automatically saves into your Obsidian or Logseq vault.

  • Clean YAML Frontmatter

    Per-book Markdown (.md) files include metadata, tags, chapter titles, and timestamps.

  • Vocabulary Export

    Exports lookups with definitions, phonetics, and context into a central file.

  • 100% Plain Text Storage

    Notes stay on your local disk as standard Markdown files—never in a locked cloud.

  • Deep Link URI Support

    Click links in Obsidian to jump directly to specific books and CFI passages.

insights

Reading Statistics & Insights

Detailed, private reading analytics and habit tracking stored locally on your SSD.

  • 12-Week Activity Heatmap

    Visual daily activity log tracking your reading consistency, streaks, and momentum.

  • Reading Streaks & Records

    Monitors your current daily reading streak and tracks your all-time personal best.

  • Reading Goals & Targets

    Configure daily reading minute goals and track annual book completion targets.

  • Per-Book Reading Analytics

    Tracks total hours read, percentage completed, estimated time left, and 1–5 star ratings.

shelves

Shelves & Library Architecture

Organize, discover, and catalog thousands of books with zero database bloat.

  • Custom Shelves & Collections

    Group books into custom shelves (e.g. Research, Philosophy, Fiction, Favorites).

  • Multi-View Modes

    Switch between visual Grid View with book covers, detailed List View, and Compact rows.

  • Multi-Criteria Sorting

    Sort books by Title, Author, Date Added, Last Opened, Reading Progress, and Rating.

  • Parallel Batch Ingestion

    Multi-threaded Rust pipeline (rayon + SIMD) imports hundreds of books in seconds.

  • Hardware Deduplication

    SHA-256 deduplication prevents accidental duplicate imports and extracts clean covers.

  • OPDS 1.2 Catalogs

    Download 75,000+ free classics from Project Gutenberg and Standard Ebooks or Calibre servers.

headphones

Immersion Audio & TTS

Listen naturally with on-device neural voice synthesis or attached audiobooks.

  • Supertonic 3 Neural Voice

    Offline neural TTS running on CPU across 10 voices and 31 languages.

  • Sentence-Level Streaming

    Starts speaking instantly while pre-fetching subsequent sentences in background.

  • Platform TTS Fallback

    Uses built-in OS speech (Android TTS, spd-say, macOS say, Windows System.Speech).

  • Audiobook Companion Player

    Attach DRM-free .m4b or .mp3 audiobooks with chapter navigation and sleep timer.

  • WSOLA Pitch-Preserving Speed

    Waveform Similarity Overlap-Add algorithm allows 0.5×–3.0× playback with natural pitch.

  • Save-as-Audiobook

    Export any open ebook into an offline audiobook in one click (Ogg Opus).

dictionary

Offline Dictionaries & Vocab

Instant word lookups without sending your queries to external web APIs.

  • Sub-Millisecond Queries (< 1ms)

    Native memory-mapped (memmap2) StarDict engine looks up words instantly from SSD.

  • Wiktionary Integration

    1-click download of English Wiktionary (800,000+ words) right from settings.

  • Custom StarDict Import

    Import any .ifo, .idx, or .dict.dz dictionary with DictZip automatic inflation.

  • Vocabulary Review Workspace

    Review words you looked up while reading, complete with phonetics and definitions.

lock

Private LAN Sync & Privacy

True data sovereignty with encrypted local networking and zero telemetry.

  • Encrypted LAN Sync

    Pair desktop and Android devices over local Wi-Fi using end-to-end encryption.

  • QR Code Device Pairing

    Quickly pair new devices with public-key cryptography—no cloud relay needed.

  • Zero Telemetry

    Zero tracking cookies, zero surveillance scripts, zero data collection.

  • Full Backup Bundle

    Export your complete library, annotations, settings, and vocabulary in one archive.

How it works

1. Add Your Library

Import your files

Drop in your EPUBs, PDFs, comic archives, or RSS feeds. Files import into a local SQLite database in seconds.

2. Read & Annotate

Highlight and peek citations

Highlight with 6 colors, draw freehand notes on PDFs, and click citations to preview footnotes without losing your scroll position.

3. Instant Vault Mirror

Plain Markdown on disk

Every highlight and note is written immediately to your Obsidian or Logseq folder as clean Markdown (.md) files.

4. Sync Over Local Wi-Fi

Private device pairing

Scan a QR code to pair your phone and tablet. Reading progress syncs directly across devices over your home Wi-Fi with zero cloud relay.

Comparison

How Theorem compares to alternatives

FeatureTheoremReadwise ReaderKindle AppApple Books
Price100% Free Forever (Open Source)$9.99 - $12.99 / month ($120/yr)Free (Tied to Amazon Store)Free (Apple devices only)
Account RequiredNone (No login needed)Required (Readwise account)Required (Amazon account)Required (Apple ID)
Where Your Notes LiveDirectly on your disk as plain .md filesReadwise Cloud (synced via API)Amazon Cloud (publisher clip limits)Apple iCloud (closed database)
Obsidian & Markdown SyncAutomatic local folder mirrorPlugin pulls from cloud APINone (Manual email or 3rd-party)None (Manual copy & paste)
Works Offline100% Offline (reading, search, TTS)Caches offline; sync needs cloudReading offline; sync needs cloudReading offline; sync needs iCloud
Text-to-Speech (TTS)Built-in offline neural voice (on CPU)Cloud AI voices (streams from web)Basic robotic accessibility voiceStandard OS spoken content voice
Supported PlatformsLinux, macOS, Windows, Android, WebWeb, iOS, Android, macOSiOS, Android, Windows, macOS, KindlemacOS, iOS, iPadOS only
Installation

Download Theorem v1.5.7

Choose your operating system. Standalone native packages with zero account registration.

macOS Universal .dmg

Apple Silicon (M1–M4) & Intel Macs · macOS 11+

Download for macOS
Linux x86_64 / arm64

Debian, Ubuntu, Fedora, Arch & generic tarballs

Download for Linux
Windows .exe

Windows 10 & 11 (64-bit standalone installer)

Download for Windows
Android .apk

Phones and tablets running Android 8+

Download for Android