GKiller
A GKiller is a tool or web search application which does something (anything) better than Google. Whether it be mapping, documents,imagery search, algorithmic search or syndication, a GKiller must not only mirror the simplicity and power of the Google search engine, it must go beyond the powers of Google and do what Google does better. GKiller is a game changer.
I'm getting tired of reading about whether Wolfram Alpha is a GKiller. I've seen Stephen Wolfram's presentations a couple of times; he's quite careful to say that it isn't. Wolframization will never kill Googling.