tee
tee is a simple stream multiplexer for nodes writable streams.
install
To install tee just checkout this repository and copy the tee.js wherever you need it. If this projects gets something that looks "ready" someday, i'll publish it at npm.
Usage
var tee = require('tee');
var target = new tee(process.stdout, fs.createWriteStream('log.txt'));
target.write('logentry');