I grabbed the package from http://flarum.org/download/
Warning: require(/Users/user/Sites/flarum/flarum/vendor/autoload.php): failed to open stream: No such file or directory in /Users/user/Sites/flarum/flarum/bootstrap.php on line 21
Fatal error: require(): Failed opening required '/Users/user/Sites/flarum/flarum/vendor/autoload.php' (include_path='.:') in /Users/user/Sites/flarum/flarum/bootstrap.php on line 21
I tried to recursively chown every files and folder but also ran into permission issues.