localhost is a special hostname that almost always resolves to 127.0.0.1. If you ask someone else to connect to http://localhost they'll be connecting to their computer instead or yours.
To share your web server with someone else you'll need to find your IP address or your hostname and provide that to them instead. On windows you can find this with ipconfig /all on a command line.
You'll also need to make sure any firewalls you may have configured allow traffic on port 80 to connect to the WAMP server.