I am looking for sites or communities where I can post my writings for reviews free of charge. Is there any?
The only link I can find on ELU is already in the Help, and simply assists with searching for services. Because services might start up and shut down without warning, it's impractical to maintain a list on this site — unlike with online dictionaries, which have proved their longevity and are actually helpful to on-topic questions.
The link is to a Google search: https://www.google.co.uk/search?q=online+proofreading+service