Hammer is a free, open-source, local-first story editor for writers, built in Kotlin with Compose Multiplatform and shipped for Android, iOS, Windows, Linux and macOS, so a single draft stays with its author across phone and desktop.

What it is

Hammer is a multiplatform writing application for building stories. It lives in the Kotlin and Compose Multiplatform ecosystem, which means one shared codebase and one interface model produces native applications for Android, iOS, Windows, Linux and macOS rather than a separate editor per platform. The project is developed by Darkrock Studios, licensed under MIT, and distributed through the Google Play Store, F-Droid, the Apple App Store and the Microsoft Store, with direct .apk and .msi builds attached to GitHub releases. The homepage is hammer.ink.

The concrete problem it addresses is draft ownership across devices. Writing tools commonly lock a manuscript to one operating system or keep it on a vendor server, which forces an author to pick between drafting on a phone and editing on a desktop. Hammer is labelled local-first and offline in its topic list: stories live on the device, and sync moves them between the platforms an author already owns. The facts do not name a specific competing product that it replaces; what is documented is the platform spread and the offline-first storage model.

Key capabilities

• Single Kotlin and Compose Multiplatform codebase targeting Android, iOS, Windows, Linux and macOS.
• Local-first, offline storage of stories, per the local-first and offline topics.
• Cross-device sync, per the sync topic.
• Story creation and long-form writing workflows, per the story-creation, writing and writing-tool topics.
• Distribution through Google Play, F-Droid, the App Store and the Microsoft Store, plus direct .apk and .msi downloads from the latest GitHub release.
• Community localisation hosted on Crowdin, project hammer-editor, with a community Discord server linked from the README.
• MIT licence, with continuous integration through .github/workflows/build.yml and quality reporting through Codacy and Codecov.

Who uses it and how

• Novelists and fiction writers who draft on an Android phone and continue the same story on a Windows or Linux desktop, relying on sync rather than file transfer.
• F-Droid users on de-Googled Android devices, who install com.darkrockstudios.apps.hammer.android without Google Play, or sideload hammer.apk directly.
• Desktop writers on Windows who install from the Microsoft Store or the .msi, and macOS users who run the project alongside their existing toolchain.
• Translators contributing locale strings through the Crowdin project, since the app ships badges for localisation coverage.
• Contributors working in Kotlin and Compose Multiplatform who build from source via the GitHub Actions build workflow.

Getting started

Install from a storefront — Google Play, F-Droid, the App Store or the Microsoft Store — or grab the direct .apk or .msi from the latest GitHub release. Downloads and project links are collected at hammer.ink.

How it compares

The registry facts list no paid products that Hammer replaces, and they name no similar open-source editors. On the evidence available, Hammer stands alone in this registry as a Compose Multiplatform story editor.

When to use it — and when not to

Pick Hammer if the priority is a free MIT-licensed editor that keeps drafts on the device and works offline on the hardware already in hand. The README is sparse — a one-line description plus availability badges — and it documents no server component, database, object storage or mail configuration, so anyone expecting a documented self-hosted sync backend has no material to plan from, and the sync mechanism itself is not described in the facts. The repository also carries 54 open issues, so teams needing guaranteed real-time multi-author collaboration or a formally documented hosted service should look elsewhere first.