They are nimble vehicles, adding a splash of rainbow colour on the roads as they take visitors on tours around the German capital.
"They" are not your common four-wheel cars, however, but instead compact, three-wheeled velotaxis, with a "driver" up front and two passengers sitting behind on tours of the city.
You find velotaxis all over Berlin - parked before the mighty Brandenburg Gate, cruising along the lush-green Tiergarten, down the fashionable Kurfuerstendamm, or perhaps en-route to the city's bustling Potsdamer Platz.
"Over 1,000 velotaxis have been exported abroad in the past four years," says Ludger Matuszewski, the Berlin-based business manager of the firm, which gave the vehicle its name back in 1997.
"It must be awfully hard for those peddling velotaxis," sighed an American architect's wife on a recent velotaxi tour of Berlin's new government quarter around the Reichstag.
Such comments are frequent when tourists make city tours. In reality, the 2007 velotaxi - named "City Cruiser2" - is equipped with an electric-powered engine which aids the peddling driver on sharp inclines, or when there are weighty passengers.
Besides its Akku and mini-motor, it also has a cell-fuelled engine and re-charger. "One, doesn't need to do much pedalling in these new vehicles," concedes a young man, as he relaxes by his velotaxi on the Pariser Platz, while waiting for customers.
The City Cruiser2 travels at a speed of 10-15 km an hour, and operates on just 300 milli-litres of methanol weekly, with minimal carbon dioxide emission.
With licensing arrangements in nine cities, velotaxis have proved particularly successful in Japan, according to Matuszewski.
"They are as crazy as we are. They are attracted to the taxi because they like its design, even when they know they could make the vehicle themselves - at far more favourable cost."
Throughout the year the CityCruisers are in service in Berlin, shuttling passengers either on scheduled city routes, or to corporate celebrations, sports events, trade fairs and congresses.
Dr Voelker Hassemer, a former Berlin Environmental Senator, actively praises the velotaxi's innovativeness, saying it combines "the performance of an environmentally sound means of transport with the awareness of a top advertising medium."
The Future Berlin Foundation has supported velotaxi development in Berlin since 1997.
Linked to the vehicle is "Advertising in motion" campaign, which has proved so successful it has spread to over 40 international locations - Paris, Tokyo and London among them.
In the process, big brand names such as Sony, PUMA, Nike, Diesel, Langnese, Mastercard, T-Mobile, Esprit, C&A now have colourful ad campaigns via the velotaxis.
In the past ten years the velotaxi enterprise has created 200 jobs in Berlin, and given big-sized leg muscles to the more than 1,000 drivers in transit throughout Germany from April to October, seven days a week.
"Since l started this job a year ago my calf muscles have certainly developed," chuckles velotaxi driver Mathias In der Reiden, proudly.
On an average day, weather permitting, Mathias, 32, reckons he covers 70 to 80 km conveying visitors about Berlin. On good days, he nets 80 to 100 euros, he says, adding, "but there are bad days, too, when l return home, having failed to earn a single euro."
Berlin' Economics Senator Harald Wolf is impressed by the city's velotaxis, saying they add to the city's sense of colourful identity and help it profit as a "tourist metropolis."
Rivalry is keen in the bile taxi business, Kai Luebeck, 26, actually named the company he created four years ago "Biketaxi."
Based in the Prenzlauer Berg district of eastern Berlin, he and another business associate now operate 27 machines, plus what he calls one "conference bike" - seating six passengers, with himself acting as "navigator!"
"The conference bike," he says, "is something of a novelty. Tourists enjoy making city tours on it, with five or six people peddling away simultaneously." Asked if he designed the bike, he replies: "No. They're made in Hanover and today are often to be seen in the bigger German cities."
"For grand city tours, the charge is 30 euros an hour, with 5 euros for short tours," he says.
"I enjoy being my own boss. I mean there are worse ways of making a living!" Lueback added.