I've recently been inspired by services like jit.si, scribble.io where you go, generate an instant link and share it with others. As an experiment on how this model can be applied for crowd management, me and a few friends have developed SimplQ.me, a website where anyone can go create a queue and use it to keep people in a... queue. :p
The web app is really simple, the first screen shows how someone can create a queue and the second screen is the queue admin page, where you can manage people who have joined. The third screen is what a person who is waiting in the queue will see.
Once people start queuing up, you can notify users by clicking on the bell icon. People can give phone numbers while joining the queue, so you can click on the person to call them. We are working on integrating with an SMS service, so that the users can also be notified via SMS. Also a design overhaul is being planned.
The frontend is built with React, backend in Java and all the code is open source and is available here on gitHub. Feel free to fork and improve if you have any cool ideas in mind :)