ERA is an centralised RSS aggregator which emails updated content to subscribers.
RSS is a way for a site to summarise its content in a machine-readable form. A site publishes an RSS feed, which contains the most recent items of content on the site (usually the last 10-20). The site's users then run a piece of software called an RSS aggregator which periodically retrieves the RSS feed and then notifies the user if the feed (and therefore the site) has changed.
ERA removes the need to run an aggregator. Once you have an ERA account, you can subscribe to feeds. ERA monitors the feeds and then emails you any changes.
It's still in its infancy, and undergoing testing. However, there's an email interface working now, if you fancy having a go. Feedback to era.feedback@indecorous.com, please.