Readest

Ebook reading has a lock-in problem. Amazon, Apple, and Google all built their reading apps as storefronts first. Your highlights, notes, and reading position live inside their silos, and the formats they favor quietly discourage you from leaving. You don’t own a library so much as rent access to one.

Readest, from Bilingify LLC, rejects that model. There is no store and no proprietary format. You bring your own files, including EPUB, PDF, MOBI, AZW3, FB2, CBZ, and TXT, and the app reads them on iOS, Android, Windows, macOS, Linux, and the web. The project is open source, built on web technologies wrapped in native shells. That is how a small developer ships one codebase to six platforms, including a browser tab.

The market position is clear once you know the neighbors. KOReader is the power user’s favorite: endlessly configurable and built for e-ink, but its interface was never designed for a phone. Polished commercial readers look better but usually charge more, read fewer formats, or treat interoperability as an afterthought. Readest sits between them. It aims for KOReader-level ambition with a modern interface, and it can sync directly with KOReader itself.

Early reception is strong, though the sample is small. The iOS App Store shows 4.5 out of 5 from 187 ratings, and Google Play sits around 4.4. Reviewers keep praising the same things: reliable cross-device progress sync, the Calibre and OPDS hooks, and natural-sounding text-to-speech. Several make a point most critics miss. Open source works as insurance against abandonment, and readers who have watched beloved apps disappear take that seriously.

The business model is free with optional in-app purchases. As we’ll see, that decision causes the app’s only real controversy.

• Universal Format Support: EPUB, PDF, MOBI, AZW3, FB2, CBZ, and TXT in one app. Comics, technical PDFs, and DRM-free Kindle-format files all go into the same library.
• Cross-Device Sync: Library, highlights, notes, bookmarks, and reading progress follow you across phones, tablets, desktops, and the browser.
• Parallel Read: Two books side by side with synchronized scrolling, built for translation work, study, and close textual comparison.
• Language & Reference Tools: Built-in dictionary lookup, Wikipedia search, and DeepL translation scoped to a paragraph, a page, or an entire book.
• AI Text-to-Speech & Speed Reading: Natural-sounding narration and a speed reading mode, plus auto-scroll for hands-free reading.
• Ecosystem Connectors: OPDS catalogs, public libraries, Calibre and Calibre Web servers, KOReader sync, and export or connection to Readwise, Hardcover, Obsidian, and Audiobookshelf.
• Deep Customization: Fonts, margins, line spacing, light/dark/sepia themes, custom dictionaries, and custom fonts.
• Library Management & Privacy: Full-text search, drag-and-drop folder import, and an optional PIN lock.

The Core Reading Loop

A reader app succeeds or fails on the boring stuff: open a book, adjust the type until your eyes stop complaining, and disappear into the text. Readest handles the fundamentals with the right priorities. Control over fonts, margins, and line spacing is the baseline any serious reader should expect. What lifts Readest above that baseline is custom font and dictionary support. If you’ve ever wanted a specific serif face or a specialized glossary for a technical text, you know how rarely mainstream apps allow it.

Light, dark, and sepia themes cover the basics. Some readers will want more granular color control, but the three-theme approach keeps the settings manageable in an app that already has a lot of them. Full-text search is the kind of feature you forget about until you need it, and then it becomes essential, especially for anyone using Readest as a research tool rather than a beach-read machine.

Sync: The Feature That Actually Matters

Cross-device continuity is why readers stay with Kindle, and it’s where most open alternatives fall short. Readest takes it seriously. Highlights, notes, bookmarks, and progress move between devices, and users report that it works.

The standout is KOReader sync. This is the most important feature in the app, and it’s buried in a long list. Plenty of dedicated readers run KOReader on Kobos, Kindles, and Android e-ink tablets because it beats the stock software. Until now, picking up on a phone meant giving up continuity. Readest closes that gap. You can read on e-ink at night, switch to your phone on the train, and land on the right page. Amazon offers this kind of handoff only inside its own ecosystem. Readest offers it across hardware you already own.

The caveats matter, though. One user asked for full file syncing, which suggests the app’s handling of the book files themselves doesn’t yet match its metadata sync. More pointedly, third-party commentary has noted friction over certain sync features sitting behind payment. I’ll take a clear stance here: charging for cloud storage capacity is defensible, because servers cost money and the core app is free. But continuity is the heart of this product. If the paywall makes basic cross-device reading feel like a toll, it undermines the app’s whole pitch. Bilingify needs to make the line between free and paid bright, obvious, and generous.

Parallel Read and the Bilingual Toolkit

The developer’s name, Bilingify, signals where this app is most opinionated, and it shows. Parallel Read puts two books side by side with synchronized scrolling. For language learners reading a novel next to its translation, students comparing editions, or translators checking their own drafts against a source, this is a real workflow tool, not a gimmick.

The surrounding tools reinforce it. Dictionary lookup and Wikipedia search handle quick references. DeepL translation at the paragraph, page, or whole-book level is the boldest option. Paragraph-level translation is the sweet spot: it gives you a crib when a sentence defeats you without taking over the reading. Whole-book machine translation is impressive in a demo but questionable for literature, where DeepL’s fluency can hide real losses in tone and nuance. Treat it as scaffolding, not a substitute for a human translator.

The obvious limitation is screen size. Two columns of text on a six-inch phone is cramped. Parallel Read belongs on tablets, and phone-only users should adjust their expectations.

Listening, Skimming, and Scrolling

Users describe the AI-powered text-to-speech as natural-sounding, which is more than most built-in TTS earns. The notable complaint is that it sometimes skips sentences or paragraphs in PDFs. That’s predictable, since PDFs encode layout rather than semantic structure and text extraction is unreliable. Predictable still isn’t acceptable, though. If you plan to listen to PDF-heavy material, expect gaps. EPUB is the safer bet.

The speed reading mode and auto-scroll serve different audiences. Speed reading suits skimming nonfiction and work documents and is largely beside the point for fiction. Auto-scroll is the quieter win, and reviewers specifically praise it for hands-free reading.

The Ecosystem Play

This is where Readest stops being an app and becomes infrastructure. OPDS catalogs and public library browsing provide legal sources of free books. Calibre and Calibre Web connections let self-hosters treat their home server as a personal bookstore. On the output side, Readwise, Obsidian, and Hardcover integrations send your highlights and reading history into the tools where you think and track. Audiobookshelf support extends the reach to self-hosted audio.

For people who build personal knowledge systems, the Obsidian and Readwise hooks alone justify the install. The cost is onboarding friction. A casual reader who doesn’t know what OPDS means faces a dense settings surface, and Readest makes little effort to hide its power-user complexity. That’s a fair trade for its core audience, but it limits mainstream appeal.

Readest looks like a modern app, which is more than KOReader can claim. The interface is clean and conventional, and it keeps out of the way of the text, which is the main job of any reader UI. The three-theme system is tasteful if not adventurous.

The web-technology foundation is both a strength and a risk. It is why Readest runs everywhere, including a browser. But web-based rendering layers can feel less immediate than fully native code, especially on older or budget hardware. User feedback doesn’t flag broad performance problems, which is encouraging. The most specific technical complaint is the PDF text-to-speech skipping, which reflects the format’s limits more than sluggish rendering. Owners of low-end Android devices should still test with their own heaviest PDFs and comics before migrating a large library.

iOS: Readest’s main rival here is Apple Books, which comes preinstalled and is highly polished. Apple Books handles EPUB and PDF well but doesn’t read MOBI, AZW3, FB2, or CBZ natively, and it doesn’t talk to Calibre or KOReader. That gap is Readest’s opening. On iPad, the larger screen finally gives Parallel Read room, and drag-and-drop folder import fits naturally with the Files app and multitasking.

Android: The more open filesystem suits Readest’s bring-your-own-library philosophy. Folder import, Calibre workflows, and sideloaded collections all feel more at home here. Android-based e-ink tablets are an obvious secondary use case, and KOReader sync makes Android the natural bridge between e-ink and phone reading.

On both platforms the experience is touch-first, built on page turns, tap-to-lookup, and text selection for highlights and translation. The PIN lock is a small but thoughtful addition for shared family tablets or readers who would rather keep their library private.

Readest is what a modern ebook reader should be: format-agnostic, interoperable, and on your side. It treats your library as yours. It connects to the tools serious readers already run instead of trying to replace them. And with KOReader sync, it solves a continuity problem the walled gardens handle only for their own hardware.

It isn’t flawless. PDF text-to-speech needs work, the feature density will overwhelm some newcomers, and the monetization line around sync needs to be clearer and more generous before the goodwill starts to wear thin. Those are refinements, not dealbreakers. For anyone who owns their ebooks rather than renting them, Readest belongs on the home screen.