How to play My Summer Car multiplayer with a friend

My Summer Car has no multiplayer of its own. The game is built around one player: the car, the village, the jobs and the house all revolve around a single person. To play with a friend you need a mod that teaches the game to show a second person and agree on who did what. Kimppa is that mod. Here is how to get started.

What you need

My Summer Car on Steam for each player. The mod runs on top of the game and does not replace it. Each player needs their own copy; Steam Family Sharing will not do.
A Kimppa licence for each player. It is tied to a Steam account and costs 499 RUB once.
Windows 10 or 11. We have not tested other systems yet.
An internet connection. You connect through Steam, so there are no ports to open and no VPN to set up.

Installing

Buy a licence on the site. You sign in with Steam while buying, so the licence is tied to your account.
Download the launcher from the payment page and run it.
On the first start the launcher asks you to sign in with Steam. You only do this once.
The launcher finds the game in your Steam library and starts it. It does not change game files; the mod is loaded in memory at start-up.

A tip for the first time: copy your save folder, %USERPROFILE%\AppData\LocalLow\Amistech\My Summer Car. The mod does not break saves, but it is a good habit, especially if you have played with other mods before.

Inviting a friend

One of you is the host, and you play in the host’s world. The host loads their save and opens a lobby; the other player accepts the Steam invite. A few seconds later the guest appears in the host’s world with their own wallet and their own needs.

Where progress is saved

Everything goes into the host’s regular saves, including the guest’s wallet and items, so next time the guest continues with the same money. If someone else hosts, it is a different world: each player has their own save, just like in single player.

What is shared and what is personal

The whole world is shared: cars, the Satsuma with every part and bolt, the shop, jobs, the house, weather, traffic and rally. If one of you drinks a beer from the crate, it is gone for the other one too.

Personal things are the ones that belong to your body and your pocket:

hunger, thirst, fatigue, dirt and how drunk you are;
money in your wallet, though you can hand it over to your friend;
fines and warrants: the police ticket whoever broke the law.

Pay for shared work is split evenly between the players who were nearby. If your friend was asleep at home, there is no share for them.

When something goes wrong

Your friend cannot take the wheel. There is one driver per car. If the seat is taken the game says so; ride as a passenger.
A hitchhiker will not get in. They look for a free seat. If both front seats are taken they sit in the back, if the car has one.
The guest does not see a purchase. Wait a couple of seconds: the host first wakes the shop up on their side, then the goods show up for both.

If the problem stays, write to support and attach the log from %LOCALAPPDATA%\Kimppa\Logs. The log usually tells us what happened without a long back-and-forth.