Websocket is actually not that complicated. A couple of headers to upgrade the request from HTTP to websocket, then framing of each payload.

But you could use something like websocketd, which spawns a process of your chioce for each client and pipes the websocket to stdin and vice versa.

https://github.com/joewalnes/websocketd

Each PHP process looks like it takes about 5 MB of ram on my laptop, so probably not the best method for 5000+ concurrent users if you use PHP, but still.