Co-op Servers
Online servers are implemented in game since 0.42.
Servers
You can connect to players from all around the world join a server or create your own to enjoy the experience of the game together. It allows you to interact with your friends. You can chat, trade and battle with each other in PVP.
Direct trading and PVP battles
Online server allows Direct trading and PVP battles.
When connected to GameJolt, there are new ways to interact with other trainers online: Direct trading and PVP battles are two unique ways to show off your Pokémon and compete with others.
Direct Trading also save time from needing to add as GameJolt friends in order to trade each other.
Where are the online server list?
Currently, there are few of them that are active. They are over here.
What is server OP
Basically, server OP allow you to manage the server. You can change the weather, seasons, mute someone, ban someone and many more.
Server command?
This list will show you what command is available to use in server. Mostly for OP only.