In Farming Simulator 2013, you can play online with a friend so he can join your farm and play with you, but he is always "guest" in your farm. What if I want him to play overnight in my farm while I'm not there? Is there any way to share the saved file or something ?
Since you host the game all the saves are on your computer. You would need to go into your documents->my games->Farming Simulator 2013 and find which save number you have been saving the game to and then send everything in that folder to your friend.
Your friend would need to place this folder in the same location and load that saved game to continue where you left off.
As for now there is a beta "server only" version : http://www.ulule.com/farming-simulator/
With this the server can run independently from you, even if no one is connected the farm keep living. This allows persistent farming worlds that run 24/7. Players can log in and play together anytime they want.
It can run on your computer for you and your friends to connect to. Alternatively you can find some "hosters" that will let you rent some servers, like http://www.nitrado.net/ or http://gameserver.gamed.de/