Most MMOs have extensive in-game text-based chat options. There’s almost always world chat, where everyone on the server can send and receive messages. Local chat is similar but keeps the chat to a specific area of the map. Players can also send whispers, which are direct messages to named players on the server or on their friends list. If they’re part of a guild, there’s usually a chat channel for every specific guild, too.
More recently, Discord has become a popular choice for online communications. The chat client allows for voice chat outside the game, which is easier for some to use than text chat. But it also has text channels, too.