Well, you could use PHP, but PHP is server side, so anytime you need the program to do something, you will have to send data to the webserver, and then the page will reload.
Another option is JavaScript. It is client side, so there is no need to have the webserver do all the work.
You could use flash, and then everything will operate seamlessly, and you could incorporate some graphics.
There is Java, which works on nearly every device, and you could make it support multiple people at the same time.
There are tons of different options avaliable, but without knowing the details of what you want to do, it is tough to point you in the right direction.