For that, I'd say Drupal.
You could use the Profile 2 module, which would allow you to add a bunch of custom fields to a user's standard profile (like skills or employment history).
So now you'd have the user's public profile page that would serve as his/her resume. Or you could just download the eRecruiter installation, but that would almost be like cheating.
To create a forum, you'd just enable the forum module, and to add any other "community" functionality, you could install organic groups.