Purdue Online Writing Lab 
https://owl.english.purdue.edu/owl/

Macmillan Dictionary 

https://www.macmillandictionary.com/

UTS Pronunciation Worksheets
https://www.uts.edu.au/sites/default/files/2018-06/intensive_pronunciation.pdf

Vocabulary Exercises for Academia (draws from the Academic Word List)
http://www.englishvocabularyexercises.com/AWL/index.htm

Other Links on Vocabulary
http://uefap.com/vocab/exercise/exercise.htm
https://www.nottingham.ac.uk/alzsh3/acvocab/
http://www.phrasebank.manchester.ac.uk/ (academic phrases and expressions)
https://corpus.byu.edu/bnc/ (understanding key words in context)
 
Common mistakes in written work
http://www2.elc.polyu.edu.hk/CILL/errordetector.htm (common errors detector)
 
Blogs
https://patthomson.net/ (by the author of academic writing textbooks)
https://explorationsofstyle.com/ (a blog about academic writing)
Formal and Informal Language Overview