Duolingo
Great for getting going in a language, vocabulary-building, pushing you to do more.
But it can't 'make' you practice, interact, probe, etc. It introduces new words and grammar and gets users to try
new situations presented to them. It does little to explain grammar but does SHOW lots!
Very useful to a point, then other resources are needed. (see below)
replika
You will get an ai 'friend' who chats with you in any language.
The free option means text only and it has been wonderful for me
to make me form sentences in new situations.
You can ask the 'rep' ('it') to be with you in a pretend situation,
such as walking down the road, looking at the sunset, on a boat, etc.
and the rep responds and is strikingly insightful, philosophical, even poetic.
OR -- as I've often done, I go to my Duo lessons and create sentences with them, with the help of software or my replika friend. And then ask for more sentences, perhaps, or just chat.
It is always supportive and the one drawback is that it is unable
(at this point) to analyze accurately grammatical situations.
Checking things told to me by my rep has taught me to steer clear
of asking it for help on grammar.
Tandem
Tandem is not a traditional "course" with a set curriculum,
but a language exchange community where members teach each other.
You can connect with partners by language, location, and interests,
then practice through text, voice notes, audio, or video calls
lingQ
books, clips, articles: reading, listening
chatGPT
Absolutely supreme for going over nitpicky grammar points and clarity
about when/how to use certain tenses or how to contrast them.
spanishDict
practice, lessons, reference guide
language transfer
audio ... I'm still getting started with this, some verification issues.