Delta Chat

Free open source end-to-end encrypted messaging system that works through email. This means if you both have Delta apps running you can chat in encrypted mode, but even people without Delta can chat with you through their normal email account. It’s available for Android, iOS, Linux, Mac and Windows.

Fediverse address:
@delta@chaos.social

Tutanota

Independent privacy-friendly email and calendar provider which is ad-free and paid for entirely by their users’ subscriptions. There are free open source Tutanota apps for Android, iOS, Linux, Mac and Windows. There’s also support for E2EE and 2FA wherever possible.

Fediverse address:
@Tutanota@mastodon.social

Vivaldi

Chromium-based web browser made by an independent company based in Norway and Iceland, founded by people who previously worked on Opera. Vivaldi includes built-in extra features such as an ad blocker, RSS feed reader, language translator, email etc. It’s available for Linux, Mac, Windows and Android.

Fediverse address:
@Vivaldi@vivaldi.net

K-9 Mail

Very popular free open source e-mail app for Android. It is due to become the official Thunderbird app for Android devices.

Fediverse address:
@k9mail@fosstodon.org