Thunderbird
Thunderbird is a free, open-source email and calendar app for Windows, macOS and Linux. The official repository for the Thunderbird desktop email client. It has 218 GitHub stars and is released under the MPL-2.0 license, and people use it instead of Microsoft Outlook.
github.com/thunderbird/thunderbird-desktop (opens in a new tab)
Data as of from the GitHub API; description from the project's repository. Report an error
- Official
- Linux
- macOS
- Windows
- Email & calendar
- Maintained
About Thunderbird
We also have documentation from this repository in a rendered version at Thunderbird Source Tree Documentation. In order to be able to build Thunderbird - you will need the Firefox repository as well as the Thunderbird repository (where this README lives). Check out our Getting Started documentation for instructions on how and where to get the source code.
Replaces
Commercial software people commonly use Thunderbird instead of.
- Microsoft Outlook
Similar apps
More open-source email clients
Papr
l0ng-ai/papr
A fast, native RSS reader — plus an agent-facing CLI so your AI agent can read, search and triage your feeds from the shell.
Active · last commit Sep 23, 2026
Email & calendarWindowsmacOSLinuxFolo
RSSNext/Folo
Folo is an open-source AI RSS reader that brings everything you follow into one calm timeline, then helps you read it.
Active · last commit Oct 24, 2026
Email & calendarWindowsmacOSLinuxFeed Flow
prof18/feed-flow
FeedFlow is a minimalistic RSS Reader available on Android, iOS, macOS, Windows and Linux.
Active · last commit Oct 27, 2026
Email & calendarWindowsmacOSLinuxMailspring
Foundry376/Mailspring
A beautiful, fast and fully open source mail client for Mac, Windows and Linux.
Active · last commit Oct 27, 2026
Email & calendarWindowsmacOSLinuxLunarBar
LunarBar-app/LunarBar
A compact lunar calendar for your macOS menu bar.
Active · last commit Oct 26, 2026
Email & calendarmacOSNetNewsWire
Ranchero-Software/NetNewsWire
NetNewsWire is a free and open-source feed reader for macOS and iOS.
Active · last commit Oct 25, 2026
Email & calendarmacOS
Is Thunderbird free and open source?
Yes. Thunderbird's source code is public on GitHub under the MPL-2.0 license, which is OSI-approved or FSF-free, so you can use, copy and change it for free.
How do I install Thunderbird?
Download it from the repository or build it from source by following the README on GitHub.
Can Thunderbird replace Microsoft Outlook?
Thunderbird is commonly used as a free alternative to Microsoft Outlook. Features differ, so check that it opens the file formats and covers the workflows you rely on before switching.