In case anyone missed this recent development, some enterprising folks have decided that trucking by yourself is pretty great, but trucking with other players is even better.
Thus Euro Truck Simulator 2 Multiplayer alpha came into being.
In short, it can be a little janky at times, latency is a bit of an issue and there isn't any AI traffic but that is all made up for by the fact that you can pass another truck going the other way and honk your horn at them and they will (sometimes) honk back! Or find yourself in an impromptu convoy across Germany, occasionally having small (or big) crashes as people rapidly slow to avoid speed cameras.
It's in constant development but it's already pretty good, so if you liked the original game but want something new to spice it up it's worth a look for sure.
P.S. head to their Facebook page for a link to download the installer, the one on their website is having issues (I'd post the link myself but I feel weird posting mega links on forums...)