Grey literature exists outside of and is uncontrolled by the usual academic and commercial publishers. It includes conference proceedings, occasional and working papers, policy papers and briefs, hearings, reports, and more.
National Bureau of Economic Research (NBER)
A "private, non-profit, non-partisan organization dedicated to conducting economic research and to disseminating research findings among academics, public policy makers, and business professionals. NBER-affiliated researchers study a wide range of topics and they employ many different methods in their work. Key focus areas include developing new statistical measurements, estimating quantitative models of economic behavior, and analyzing the effects of public policies."