There are several other options available to scientists to avoid predatory publishers. Among them is the Directory of Open Access Journals (DOAJ). All journals in this directory exercise a form of peer-review or editorial quality control to guarantee its content. Also look out for the DOAJ Seal indicating a high level quality standard.
Open access journals with an impact factor are covered by Web of Science and Scopus. Very often open access journals are new and therefore do not have an impact factor yet. Because of that, initiatives have recently been started to develop other quality criteria for open access journals.
Another initiative is the Quality Open Access Market (QOAM). It values a transparent peer review process as an important criterion. QOAM publishes Valuation Scorecards, which allows authors to share their experiences with scientific journals. With these cards libraries provide an opinion on the transparency of the websites of open access and hybrid journals. QOAM contains 23.000 journals and 7.300 Basic Score Cards and 2600 Valuated Score cards as of October 2016.
Lastly there is Think Check Submit. Think Check Submit is a fairly new campaign website to help researchers identify trusted journals for their research. It is a simple checklist researchers can use to assess the credentials of a journal or publisher.