You can control PiFace Digital from a web browser (or any network enabled device) using the simplewebcontrol.py tool.
You can start the tool by running the following command on your Raspberry Pi:
$ python3 /usr/share/doc/python3-pifacedigitalio/examples/simplewebcontrol.py
This will start a simple web server on port 8000 which you can access using a web browser.
Type the following into the address bar of a browser on any machine in the local network:
http://192.168.1.3:8000
Note
Relace 192.168.1.3 with the IP address of your Raspberry Pi.
It will return a JSON object describing the current state of PiFace Digital:
{'input_port': 0, 'output_port': 0}
You can set the output port using the URL:
http://192.168.1.61:8000/?output_port=0xaa
You can specify which port you would like simplewebcontrol.py to use by passing the port number as the first argument:
$ python3 /usr/share/doc/python3-pifacedigitalio/examples/simplewebcontrol.py 12345