ThreeStrands

ThreeStrands is a keyboard-first, local-first desktop email client for people who spend much of their day in email. It brings three strands of work together in one app (mail, tasks, and your calendar) so follow-ups and scheduling stay beside the conversation instead of slipping between apps.

ThreeStrands works with Gmail and IMAP/SMTP accounts on macOS and Linux, including Proton Mail through Proton Mail Bridge. It connects directly to your providers: there is no ThreeStrands account or server, sign-in credentials stay in your operating system's keychain, and your messages and search index stay on your computer.

Website and docs: www.threestrands.app

Early release. Only the macOS app is used and tested regularly right now.

Mail, tasks, and calendar in one place

• Mail. Every common action has a shortcut, and a command palette (⌘K) has the rest. Triage in batches with undo, split newsletters and other high-volume mail into their own tabs, and search all your mail locally, even offline. Actions you take offline sync when you reconnect.
• Tasks. Turn a conversation into an action, a follow-up, or a waiting-for, and link it to a quarterly or yearly goal. A linked follow-up completes on its own when the reply arrives.
• Calendar. See your day or week from Google Calendar next to your mail, answer invitations, and use Find Times to put open slots, based on your working hours, into a reply.

Around those three, ThreeStrands also includes:

• Contacts with groups, birthdays, and Keep in Touch reminders for people you don't want to lose touch with.
• Files for browsing every attachment you've sent or received.
• Trust checks, run on your computer, that explain suspicious senders, links, and attachments.
• Optional AI for summaries, reply drafts, thread chat, and draft review. It's off until you turn it on, and then it uses your own provider and API key with no ThreeStrands server in between.

See the help guides and compatibility and limitations for current behavior and setup instructions.

Install

Download the latest installer from GitHub Releases:

• macOS: the .dmg for Apple Silicon (aarch64) or Intel (x64).
• Linux (x86-64): a .deb, .rpm, or .AppImage package.

Launch ThreeStrands and add a Gmail account with Google sign-in, or connect an IMAP/SMTP account in Settings → Mail Accounts.

Product principles

1. Every common action is available from the keyboard.
2. The interface responds immediately, including on unreliable connections.
3. Users can see and control what is synchronized or sent to optional services.
4. Provider-specific behavior is isolated behind a tested capability contract.
5. The desktop client connects directly to mail providers and requires no project-operated backend. Optional, end-to-end encrypted cross-device sync replicates application-owned workflow data through storage the user chooses.

Cross-device sync is described in docs/cross-device-sync.md. It never carries mail, provider credentials, or AI keys.

Building from source

To build ThreeStrands yourself or contribute, see DEVELOPERS.md.

Independent implementation

ThreeStrands uses its own name, visual identity, product language, and implementation. It learns from established interaction patterns across the email category without copying proprietary code, assets, or trademarks.

License

Copyright © 2026 OpenArc LLC. ThreeStrands is source available under the PolyForm Perimeter License 1.0.1.

You can inspect, build, use, and modify the software for permitted purposes, including personal and internal business use. Copying and redistribution are allowed subject to the license's conditions, including keeping the license and required notices. Providing others with a competing product built from this software is prohibited, even if that product is free.

The source is available so you can inspect how ThreeStrands handles your mail and credentials. This is a source-available license with a noncompete restriction, rather than an open-source license. The full text in LICENSE controls; third-party dependencies remain subject to their own licenses. OpenArc LLC may offer separate licenses for uses outside these terms.