Online games are often about immediate communication either spoken or typed in the heat of battle or survival. There are some online games that encourage communication much more like writing a letter to someone.
These games offer players the chance to write a note and then place it in the game world for others to discover. They can also, of course, also read messages and notes from other players.
With a little guidance it can be a lovely way to introduce children to the skill of letter writing, as well as engaging with other players online without the usual bad language (although that can happen here too).
Games like Subnautica, offer the ability to leave time capsules for others, that include a handful items, a short text message and a screenshot. Similarly, games like, Dark Souls and Demons Souls enable you to leave messages for other players to help them with tips. In Nier Automata you find the bodies of other fallen players that have a customized message left on them when they met their end.
Other games weave the letters and messages into the gameplay. Kind Words, for example, is a game all about responding to letters that other people have sent. The Things We Lost In The Flood, builds its play around the ability to send and find messages in bottles. In Animal Crossing New Horizons on the 3DS you can also put messages in bottles for other players to find.
This list includes 7 games from the last 21 years, with 385 likes. They come from a range of different genres and play-styles and are all good games if you want to write letters to strangers.