The Embedded Discovery Service (EDS) allows a Service Provider to run a discovery service within their own site. As such the discovery service can look like any other page on the site and thus not be as jarring to a user as being redirected to a totally different, third-party, discovery service site.
The EDS is a set of Javascript and CSS files, so installing it and using it is straight forward and does not require any additional software.
Note: The EDS is technically independent of the SP software, but the JSON feed it relies on is produced in general only by V2.4+ of the SP. The same format produced by some other source should work fine, however.