Photon
Photon is a multiplayer solution for Unity, Unreal, and various other game engines
Photon Products
Realtime
https://www.photonengine.com/en-US/OnPremise
https://doc.photonengine.com/en-us/realtime/current/reference/playfab
Server
PUN
https://www.photonengine.com/en-US/PUN
Bolt
Unity Package:
https://assetstore.unity.com/packages/tools/network/photon-bolt-free-127156
Quantum
Comparing Products
PUN vs Bolt: https://doc.photonengine.com/zh-TW/pun/current/reference/pun-vs-bolt
Tutorials
References
Unite Europe 2017 - Photon vs UNet: multiplayer architecture explained