Altmetrics is the creation and study of new metrics based on the Social Web for analyzing, and informing scholarship. (altmetrics.org)
Altmetrics, short for "alternative metrics" are a variety of alternative tools to measure research impact. These tools have been created to address a variety of criticisms of traditional metrics. These tools account for a broader range of scholarship, the prevalence of web-based scholarship, such as online blogs, and the authority of readers. Read more about altmetrics in Altmetrics: A Manifesto.
The Problem With Traditional Metrics
Altmetrics attempt to mitigate the problems with traditional metrics by using different methods to evaluate research impact. Every tool has specific benefits, but in general, altmetrics are:
Altmetrics can be applied to different types of research output such as articles, blog posts, nanopublications, and datasets. Some journal publishers have adopted altmetrics to assess the impact of individual articles. For example, the Public Library of Science has implemented article-level metrics (ALM) to gauge the impact of its journal articles. As noted in the SPARC primer, ALM has these advantages over journal-based metrics:
Nevertheless, ALM has its own share of limitations. Just like journal-based metrics, it is prone to manipulation. Moreover, it is unable "to make distinctions of quality and intent within the collected feedback a scholarly output receives."
There are countless free altmetrics tools available on the web.
You can also view the Public Library of Science's Altmetrics Collection for more information on altmetrics tools.