Impactstory is an altmetrics service aimed at authors and researchers, who want to monitor the altmetric scores for their own articles, datasets and other research products themselves. Impactstory was founded in 2011 by Heather Piwowar and Jason Priem, who also coined the term altmetrics in 2010. While it is an incorporated non-profit organisation, mainly funded through philanthropic grants, their service isn't free. Since August 2014 Impactstory has been charging $10/month or $60/year to create a sustainable model for their service, so they can keep it running and keep on developing new features independent of any future philanthropic grants.
So what does your subscription get you? It provides you with a place in which you can link all of your research output together and monitor the amount and sort of attention it receives online. You'll receive notifications of any changes and you can use your profile as part of your online CV. You can add new items automatically by linking your Impactstory account with your ORCID, Figshare, Slideshare or other platforms, or you can add them manually to Impactstory. Once you've done so your profile homepage will show selected works and you can drill down by category and title. Holly Bik's profile is a good example of what an Impactstory profile might look like and what sort of information it provides.
Impactstory plays well with other services, allowing you to connect to many third-party applications and using API's from many third-parties, such as Altmetric.com, Figshare, ArXiv, Scopus and more, to compute metrics themselves. They aren't a one-stop shop, however, as they themselves are the first to acknowledge, instead they encourage researchers to seek out a multitude of possible metrics, to create as full and nuanced a picture of their impact as possible. Impactstory, like Altmetric.com, is a strong proponent of the idea that altmetrics aren't replacements for traditional bibliometrics, but are supplementary to them.