It could be [1]. IMO, it sounds more like something slapped on top of Flask. You will find similar packages for Django, Pyramid and so on. Tornado feels natural in this sense as it aims to be asynchronous right off the bat.

See also, aiohttp [2] which seems very promising (Python 3.3+). As an aside, I've never seriously considered Python 3 till now after taking a look at aiohttp.

[1] https://flask-socketio.readthedocs.org/en/latest/ [2] http://aiohttp.readthedocs.org/en/stable/web.html