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.
Geary - Geary is an email application built for GNOME 3.
Babble - A more personalized social network
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
LanguageBeast.com - Study English synonyms and antonyms to enrich your vocabulary
Airmail - Airmail is a lightweight and lightning fast mail client for Mac.