Hmmm. Back when I lived in the States, the word carpooling was used as a concept of a regular if not daily thing for people going to work or school along the same route. Finding riders for a longer trip could also be called car-pooling but was usually referred to it as ride-sharing. Not sure if the usage of the words has evolved since then. Very different thing to organize a regular thing than an occasional one-off trip. In Germany I haven’t really heard much of car-pooling but it would be a personal thing if one just happens to have neighbors that share the same route. But since public transportation is so much better in Germany than the States, it is not a big deal here.
Ride-sharing however has a tradition in Germany, especially amongst young people like students. Most cities at least used to have a place called a Mitfahrzentrale or ride-together-center which would match people offering and needing rides. I took some riders many years ago and then gave up on it. The problem is that one had to negotiate a time to meet, which usually meant a compromise to my actual wishes and then a number of times the people simply didn’t show up. In the end, the amount of money involved didn’t outweigh the inconvenience. It can be a way to meet people but who knows if you will like them. And the likelihood of finding just the right amount of people wanting to go to just the same place at the same time and day is pretty hit and miss. I remember one time taking a couple of people from Stuttgart to Munich but their destination was somewhere much farther. They didn’t find someone going there so we got matched. So when arriving in Munich I had to drive out of my way to get them to the main train station and they had to continue the rest of their trip by train anyway. It was not really convenient or cost-effective for any of us.
Blablabla cars is such a Mitfahrzentrale and seems to be active in a number of European countries. Never used it myself but see no reason it would be any better than what was offered in the past. If everything really fits for all involved then OK, but I personally wouldn’t bother with it. Flex-bus, or booking train tickets well in advance for a discount price or getting group tickets can be similar in price and more reliable.
Beppi mentioned Stadtmobil andCar2go. These are not ride-sharing but car sharing organizations. It is more or less renting a car but one joins the club and then goes online to reserve a car when one needs it. They are alternatives to owning one’s own car – not to share rides per se. I am a member of Stadtmobil, so if I really need a car rather than public transportation, this is where I get one.