TigerGammon is a free online Backgammon server. You play against humans or bots.
The simplest way to connect is using telnet:
telnet ti-ga.com 4321
If you prefer a graphical user interface, you'll pick from a bunch of available rich clients which satisfy the TigerGammon API. Of course you are here to see the HTML5 client, but if you are interested look at this list of rich clients, compatible to TigerGammon.
This repository contains the code for an HTML5 client. The setup for your own client is described in the wiki.
See a prototype installation of this client on TigerGammon.
Copyright (c) 2013-2014 Andreas Hausmann. See LICENSE for information (AGPL).