Unity Multiplayer, Phaser+Firebase
Create real-time, networked games
Unity Multiplayer is the simplest way to create multiplayer games for Unity. It’s fast to implement and highly customizable. Unity-provided servers ensure that your players can find and play with each other.
FREE: Unity Personal/20/Concurrent players
Phaser, … + Firebase
100 Simultaneous connections
Unity and firebase : https://firebase.google.com/docs/unity/setup