1. Journals which publish open access without charging authors article processing charges are sometimes referred to as diamond or platinum OA.
2. Since they do not charge either readers or authors directly, such publishers often require funding from external sources such as the sale of advertisements, academic institutions, learned societies, philanthropists or government grants.
3. Diamond OA journals are available for most disciplines, and are usually small (<25 articles per year) and more likely to be multilingual (38%). (From Wikipedia)