Monitter.com is a twitter monitor, it lets you “monitter” twitter for a set of keywords in real-time, filtered by location.
The original monitter website has changed and iterated a little in the past 3 years. It’s a little more advanced than it was to begin with.
The monitter widget, offered for free is currently in use on over 1500 websites around the world and has been used for wall displays at numerous tech conferences over the years.