Beall's list was a list of predatory journals and publishers, originally published by Jeffrey Beall, whose site was unfortunately taken down. See: https://www.insidehighered.com/news/2017/01/18/librarians-list-predatory-journals-reportedly-removed-due-threats-and-politics
Preadatory journals are journals which publish garbage papers, basically selling "scientist credentials" for those who are willing to pay.
The latest version for single, standalone journals (updated January 9th, 2017) is at standalone_journals.md.
The latest version for publishers only (updated December 31st, 2016) is at publishers.md.
PR's welcome!