Duolingo is a free language education application and website that offers language learning courses in over 30 languages. It provides users with an effective and enjoyable language learning experience, with interactive lessons, real-time feedback and immediate rewards. The app and website have an extensive range of courses that cover reading, writing, speaking, and listening skills. The courses are designed to move at a pace that suits the user's learning ability and preferences. Duolingo also offers additional features such as Power-Ups (which offer extra practice on specific topics), a leaderboard, and various badges and rewards to help motivate users to continue learning. Duolingo is an easy-to-use, comprehensive language learning resource that is suitable for both beginners and more advanced learners.
Anki is great, but it's for learning something on your own. If you want to learn a language with Anki, you will still need a book or something to learn the grammar. Duolingo is very accessible and you can read up on grammar before doing a lesson. It's actually a great combination. Duolingo for learning grammar, Anki for studying words.
Actual spacing repetition algorithm for reviewing words: http://memrise-users.wikia.com/wiki/Memrise_Spaced_Repetition_Intervals. The algorithm seems to have been slightly improved (adding shorter intervals). The 6-step process for learning (planting) words is better than DuoLingo's approach, which often simply throws the new/unknown words as orange (without pictures) in a typed translation practice exercise.
Memrise only teaches vocabulary.
Limit your learning to 3000 words, while Duolingo is completely free, with no vocabulary limit or any basic functionality. The only cost comes from the purchase of additional services such as Tinycards, etc.
I like rosetta stone. It's great to use this program when you are just starting to learn a language. It's amazing that you don't need to translate it into your native language. You learn it as a child your first language. And it's good for pronunciation. But it is very expensive.
Discontinued The service is still available, but the author has abandoned its development.
It makes language learning fun, so I'm sticking with it.
Only available in some area of the world. If you are from an English speaking country, it will not work for you.
Anki
Memrise
Busuu
Lingvist
Rosetta Stone
Readlang
Vocabulary.com
AnkiApp
LinguaLeo
Flowlingo
Mondly
Clozemaster
Hello-Hello
PIMSLEUR UNLIMITED
TeamSpanish
Mango Languages
Babbel
Vocabla
Agenda Mahala
MosaLingua
Duolingo teaches grammar, unlike Anki. Anki is flash card software. Duolingo's thumbnail service (tinycards.duolingo.com) is flash cards.