WebSocket with free RDMBS (PostgreSQL, SQLite, etc) and without JavaScript ecosystem
Update 01/23/17: I wrote an application called postgresql2websocket in order to send PostgreSQL notifications over websockets using Python 3 with asyncio + aiohttp + asyncpg https://github.com/frafra/postgresql2websocket; you could combine it with PostgREST in order to have both standard REST APIs and realtime updates using WebSockets.
As far I know, there is no HTTP server extension for using SQL databases with Websockets without anything in the middle.
You can use Python on the server side, like this: Real Time Web Apps with (just) Python and Postgres. I think it could be improved thanks to aiopg. If you don't need Websockets, you can just use ngx_postgres.
If you like Django, Django Channels will be probably included in Django 1.10 (Redis/in-memory/... layer for channels and SQL backend).
You could use SQLite, but bear in mind that you have to implement a separate server side publish/subscribe mechanism (like Django channel does), because SQLite doesn't have one.
If you're just interested in pub/sub over Websockets, you could use Webdis (Redis-based solution): it would be probably lighter than a full SQL database.