PubMed Commons has been a valuable experiment in supporting discussion of published scientific literature. The service was first introduced as a pilot project in the fall of 2013 and was reviewed in 2015. Despite low levels of use at that time, NIH decided to extend the effort for another year or two in hopes that participation would increase. Unfortunately, usage has remained minimal, with comments submitted on only 6,000 of the 28 million articles indexed in PubMed. Read more here.