The best Calendar alternative to Mailspring is Thunderbird, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to Mailspring and nine of them are Calendar Apps so hopefully you can find a suitable replacement. Other interesting Calendar App alternatives to Mailspring are Betterbird, Evolution, Microsoft Outlook and eM Client.
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.
Evolution is a personal information management application that provides integrated mail, calendaring, address book and task list functionality.
Streamline emails, calendars, contacts, and task management with a smart inbox prioritizing critical messages. Includes calendar scheduling, third-party app integration like Facebook, Dropbox, and Trello, and support for Microsoft Exchange, Outlook.com, and Gmail, ensuring efficient task and email handling.
eM Client is a full featured e-mail client with a modern and easy to use interface. eM Client also offers calendar, tasks, contacts, notes and chat.
emClient is wonderful for power users who like to change fonts and styles. However, I cannot swipe on mac. Swipe only works for Windows.
E-mail app with all the great features: swipes (long/short), snooze, add (multiple) attachments from the cloud, support for various e-mail services and more.
Seems to work very well on iphone.
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.
Foxmail is a free POP3 and IMAP4 e-mail client in English and Chinese for Windows systems.
The free Zimbra Desktop client allows you to meld the online and offline worlds – storing and synching your email, calendar, contacts, files and documents in the cloud, yet having them locally accessible when on the road.
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Thunderbird is free, stores nothing in a cloud service, so you control your email and the storage of your personal data. It supports encryption (natively, now) and with plugins is able to work with GMail and Exchange accounts without giving all your info to those behemothim. Easily customized mail rules allow you to route mail easily where you want it, and even without plugins it can easily protect against unwanted attachments, etc.