The best open source alternative to Microsoft Mail and Calendar is Thunderbird. If that doesn't suit you, our users have ranked more than 50 alternatives to Microsoft Mail and Calendar and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to Microsoft Mail and Calendar are Betterbird, Fossify Calendar, Evolution and SeaMonkey.
Cross-platform email client supporting multiple identities, chat, and strong filtering. Extend functionality with add-ons like RSS/Atom feed readers and PGP support.
Betterbird, a soft fork of Mozilla Thunderbird, improves user experience with advanced features, bug fixes, security patches, and multi-row descriptions similar to Outlook. Compatible with multiple platforms and can be used alongside Thunderbird, sharing the same profile.
Your privacy-aware, open-source calendar with intuitive design and multi-platform syncing.
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
Web-browser, advanced e-mail, newsgroup and feed client, IRC chat, and HTML editing in one application. Itis built on the open source Mozilla Gecko engine, the same code which underlies Thunderbird and is the base for the Firefox browser.
Geary is an email application built around conversations, for the GNOME 3 desktop.
Email and news client on GTK+ foundation featuring quick performance, extensible plugins, secure protocols, advanced filtering, strong folder and contact management, lightweight design, powerful search, customizable interface, multi-language support, and encryption.
Mailpile is a modern, fast web-mail client with user-friendly encryption and privacy features. The development of Mailpile is funded by a large community of backers and all code related to the project is and will be released under an OSI approved Free Software license.
Right Calendar app is a versatile scheduling tool that offers unparalleled flexibility to its users. One of its standout features is that it is built on an open-source platform. This not only ensures transparency but also allows for constant updates and bug fixes from a...
Wino is a lightweight native mail client for Windows 10/11. It is still in active development. Main motivation for this project is to replace Mail & Calendar for Windows with modern Windows design without using web technologies for speed.
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Thunderbird's more stable in my experience, certainly more capable, the 2023 UI update has improved matters quite a bit, plus I had a much easier time tying it to my Nextcloud calendar and contacts. It's a bit heavier, but that's balanced out by the other benefits. Plus Thunderbird will also run on other platforms.