When we do single page application, the webserver basically does only one things, it gives some data when the client asks them (using JSON format for example). So any server side language (php, ror) or tool (apache, ningx) can do it.
But is there a language/tool that works better with this sorts of single page applications that generates lot of small requests that need low latency and sometimes permanent connection (for realtime and push things)?
If you want a lot of small requests in realtime by pushing data – you should take a look at socket type connections.
Check out Node.js with Socket.io.