There is a Stack Exchange community for code reviews: https://codereview.stackexchange.com/
However they have some strict rules on what is allowed so it may not be suitable for open source projects. Two problematic ones are: 1) The poster must be the author/owner of the code. You, for example, can't post code that someone else has written. 2) All code that is to be reviewed must be included in the post. You can't just link to a repository.
There is a Stack Exchange community for code reviews: https://codereview.stackexchange.com/
However they have some strict rules on what is allowed so it may not be suitable for open source projects. Two problematic ones are: 1) The poster must be the author/owner of the code. You, for example, can't post code that someone else has written. 2) All code that is to be reviewed must be included in the post. You can't just link to a repository.