While I was multitasking on the net and came across this interesting website which offers a free online course consisting of a comprehensive revision of English grammar.
It is designed for those already fluent in English, but who want to improve their writing. It covers punctuation and grammar, from commas and colons to adverbs and prepositions.
It says that by completing this course, you will see a marked improvement in your written English!!
Each section breaks down the rules into easily assimilated explanations. There is a section on spelling. This course is ideal for anyone looking to improve their written and indeed spoken English.
It also contains audio, so ensure that you have speakers or headphones ready. A text transcript is also available. Isn´t is promising?
Are you interested? Here is the link