Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
LanguageBeast.com - Study English synonyms and antonyms to enrich your vocabulary
Geary - Geary is an email application built for GNOME 3.
Babble - A more personalized social network
The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.