FWIW, I'm working on something similar in Lua, which uses libevent for high performance on Unix but also has a pure Lua (based on LuaSocket.select) backend for portability. I haven't tested it on Windows yet, but I don't expect any issues with running it there, and I'm planning on supporting it as a platform (for developing convenience, not performance).

It's reasonably complete, but its development is being driven by another project (a distributed filesystem of sorts), and it's still changing too much. I hope to have it released in a month or two, but I'm also in the process of buying a house, and that's keeping me plenty busy.

If you're interested, learning Lua should would be pretty straightforward. It sounds like you're already proficient in Javascript, and they have quite a bit in common.