Well-known language learning app with courses for many languages. Great for quick vocabulary practice drills, if not for learning to conjugate verbs. If you accept giving it the power to send notifications, will nag you on the daily to get a practice sesh in (though it'll give up after a while if you ignore them).
Has the freemium model of letting you do a certain number of courses free each day, but then you have to wait or subscribe to the unlimited Plus service.
Duolingo partners with many educational institutions to give students free unlimited service and share your results with your educational institution. You may want to sign up with an .edu email address.
It's time to get your Invitation.codes account too 😎