I haven't seen this mentioned here, so I'm sharing:
It *looks* like it's meant for comparing GSA vs. ___________, meaning that we
may not be able to use it to compare any search engine to any other search
engine, but I haven't double-checked. Even if it's limited to GSA vs.
____________, one can look at the UI and functionality and simply build an app
that does the same, but is not limited to GSA.
Sematext :: http://sematext.com/ :: Solr - Lucene - Nutch
Lucene ecosystem search :: http://search-lucene.com/