All the PLoS journals are open-access. Not sure what their requirements are. Other journals typically let authors opt-in for their articles to be open-access (free) if the authors pay a large fee (eg $2000 IIRC). The journals must be quite a racket; the authors pay the publishers, and the subscribers pay the publishers, and the advertisers pay the publishers, and the editors and reviewers work for free.
All the PLoS journals are open-access. Not sure what their requirements are. Other journals typically let authors opt-in for their articles to be open-access (free) if the authors pay a large fee (eg $2000 IIRC). The journals must be quite a racket; the authors pay the publishers, and the subscribers pay the publishers, and the advertisers pay the publishers, and the editors and reviewers work for free.