Ask HN: Useful Frameworks/Approaches for Simple Number-Tracking Webapp?

I need to a build a webapp that allows any number of web-based clients (on smartphones) to increment/decrement a number. Each client's current number should be stored on a server so another app can read the list of current numbers and visualize the results in real time.

I haven't done much in the webapp space so am looking for tech suggestions on ways to about this.

I figure I could certainly do PHP/MySQL, but I want an ajax feel to the app (no page reloads). I've noticed options like Firebase/Meteor/Derby and am wondering if that might be a good way to go---avoid the DB all together. Are there other options I should be looking at?

Thanks for any help.