Forza Horizon 2 is delved into in during the Microsoft Gamescom. We learned more about the integration between online and single player, including the fact that players and their friends will be sharing the same tracks simultaneously — whether or not said friends are online. You can race against friends in this fashion at any time.
There are car meets — social places you can show off your car and embark on road trips from. You can also join a Car Club in a feature called Car Fuel, which gives you rewards and bonuses. More details on that will be revealed at a later date.
On a side note, Formula E and the Rolls Royce Wraith is coming to Forza Motorsport 5 starting today, which is good news for players. The trailers for both games have been posted below for your convenience.