WordPress repository contains a lot of outdated plugins which haven't been updated in over 2 years. For example: http://wordpress.org/plugins/post-star-rating/
This means that they no longer supported by their authors and may have compatibility issues when used with more recent versions of WordPress.
There are thousands of interesting plugins which would be great to support and update. But how can another WordPress developer become contributor for a specific plugin which is outdated, in order to support it and fix compatibility issues, etc.?
Need to contact plugin author directly and ask a permission for contributing? But if there are no contact information, or this information is outdated, or the author doesn't respond?