Free online courses in English and other languages, with pronunciation and practice activities. Has app for Apple and Android, making it very useful for self-study.
Wilingua is a good tool for students from A1 to B2. It has apps for Android and Apple. The free account offers grammar, lessons and readings. For listening and other features you have to go premium. It offers 30 days of free premium access.
Online dictionary of collocations that also has an app version. Very useful for finding out not only what words mean, but also seeing how they are used.