CelesteNet is an online multiplayer mod for Celeste. It lets you chat with other players in-game. With it, you can also play Celeste maps, vanilla and custom, together with friends and strangers. It is possible to create public or private channels, limiting the players you can see and interact with. CelesteNet is commonly used for races.
To join CelesteNet, download the mod, then turn the "Connected" option in Mod Options on. This will connect you to chat, and starting any map will show you the players currently there.
A channel in Celestecord is dedicated to CelesteNet.