Word Bucket has been a mobile language-learning app and has just now unveiled a website version.
It has several different languages available, and the exercises and games appear pretty similar to ones found in other sites.
The nice feature it has that many others do not is the ability for teachers to create virtual classrooms and monitor student progress. That tool, as well as the entire site, seems to be free.
I’m adding this info to The Best Sites That Students Can Use Independently And Let Teachers Check On Progress, which has grown to an insane length.