Tweetpulse is a project mainly written in JavaScript, it's free.
This isn't worth looking at yet. The name will also change.
Remember to make a settings.js that exports a settings object containing 'username', 'password' and 'track' (which is an array containing the firehose filter terms).
Also, this depends on twitter-node but it can't be installed via npm. Check out the readme on the repo's page for install instructions.