Joe Sullivan sent in vorbis.js (GitHub: itsjoesullivan/libvorbis.js, License: MIT), a project based on several others that produces Ogg Vorbis from PCM data. It uses Emscripten, and has an event-based API. There's a full example in the readme, which demonstrates how to configure the necessary memory buffers and encoding options.
Joe has also made a project called iago that can stream Ogg using web workers.
Atom is Open Source
Atom is now free and open source. The announcement includes the minor revelation that there are now over 800 Atom packages.
I've seen people on Twitter running the Linux version, but people are still dubious about Atom's performance and the 2 MB file limit. Making it open source seems like a solid first step to creating sustained interest, but it has a Google Wave feel about it.