If a user modifies a value, change it in real time on all the apps

This is just a question regarding the concept so I'm not looking on code snippets or something similar because I'm not a programmer but rather...let's say the product owner so I need to know what it takes to achieve this before talking with the developers (which I need to find first).

So here it is: I am thinking on creating an app compatible both with iOS and Android which (amongst other things) will display a value with the following characteristics:

1. This value will be visible to all the users that are running the app
2. If a user clicks on a particular button, the value is incremented.
3. If the value is incremented, all other users will see the new value in real time.
4. The value can be changed thousands of time per second, deepening on how many users are clicking the button.

Again, I'm mainly interested in the concept so any suggestion will be appreciated. For example since the value will get updated so many times per second, how do I store/modify it? Or how can I push it so fast to all the apps?