does not have an official multiplayer mode. The only way to play with others is through a fan-made mod called MOP (My Summer Online)
If you are designing or looking for a "Cracked Multiplayer" feature set, these concepts address the most common player frustrations and technical needs: My Summer Car Cracked Multiplayer
: Even with a cracked version, most of these fixes require Steam to be running in the background (often using a "Spacewar" workaround) to handle the networking. Common Issues and Limitations does not have an official multiplayer mode