Plum Analytics was an early mover in altmetrics, gathering a broad range of usage measures to help give researchers a detailed picture of the impact of their research.
Elsevier plans to incorporate Plum analytics into its existing research products (including Mendeley, Scopus and ScienceDirect) and its leading journal and society partner sites.
Source: Research Information.
Todd Carpenter of NISO has written an interesting analysis of the announcement, stating that the acquisition reinforces the distinction between metrics "of and for the library space" (usage of journals etc) and metrics developed to meet the specific needs of scholarly research. You can read his article on Scholarly Kitchen here.