Mu4e - Starting with version 0.9.8, mu provides an emacs-based e-mail client which uses mu as its back-end: mu4e.
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.
Mutt - Mutt is a small but very powerful text-based mail client for Unix operating systems.
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