Make sure you are using a recent version of Google Chrome, at the moment this only works with Google Chrome Canary. You also need to enable Web Audio Input under about:flags.
There are no servers involved, only Web Audio API and WAVs are passed around as binary Blobs.
Make sure you try editing a sound, there's a fairly full featured editor tied in (thanks plucked/html5-audio-editor).
Also before you enable microphone input either plug in headphones or turn the volume down if you want to avoid ear splitting feedback, especially while playing back already recorded sounds!
Finally be warned that HTML5 playback sound volume is set to maximum by default, so make sure turn it down!
Record monitor volume:
Change the volume of the selected audio sequence with the given gain multiplicator.
Adjust the volume to the maximum of the selected audio sequence.Apply
Silence the selected audio sequenceApply
Create a linear fade int of the selected audio sequenceApply
Create a linear fade out of the selected audio sequenceApply