Nice tool. I don't think I have seen a web-based version yet.
Line-in and microphone oscope applications have been around for a long time. There is one for Linux (http://xoscope.sourceforge.net/, sorry for the Sourceforge link) that can go up to eight channels if you have the audio inputs for it. Note that you can get two channels on a stereo line-in (see http://www.ledametrix.com/oscope/ for a two channel probe circuit).
Edit: Further note, these types of scopes typically have their bandwidth limited to the range 20Hz - 20kHz. These are audio channels, after all.
Line-in and microphone oscope applications have been around for a long time. There is one for Linux (http://xoscope.sourceforge.net/, sorry for the Sourceforge link) that can go up to eight channels if you have the audio inputs for it. Note that you can get two channels on a stereo line-in (see http://www.ledametrix.com/oscope/ for a two channel probe circuit).
Edit: Further note, these types of scopes typically have their bandwidth limited to the range 20Hz - 20kHz. These are audio channels, after all.