Somewhere between a Matchbox car and your daily driver sits a perfect balance of whimsy and fuel economy. Microcars are lightweight vehicles for economical urban commuting. They can seat up to four passengers; they have at least three wheels; weight limits may depend on legal classifications, but generally they’re under 500 kilograms (roughly 1,100 pounds); and their engines are under 700 cubic centimeters, which means they might get 70 miles per gallon or better.

In Portland, Ore., Mark Hatten is the founder of a one-man automotive repair shop, MPH Specialties. He caught the microcar bug by chance three decades ago. “I was given a 1966 Subaru 360 sedan by a good Japanese friend,” he said. His friend’s work visa was up, and he had to return to Japan. “I could have the car for free, as long as he got to ride in it when he returned 10 years later.” It sat for eight years. “I didn’t know how to fix it,” Mr. Hatten said. “I thought our relationship would cease.” But he got to work.

He found used parts to rebuild the engine; he fixed the brakes. “Once it was driving, it was the most fun car ever,” he said, and added, “I still drive it today, 34 years later.” There is nothing else like a microcar: “They’re challenging and quirky,” said Mr. Hatten, who plays unicycle hockey in his spare time. “Check your ego at the door.” They’re rare on city streets, and for some good reasons. But still, Mr. Hatten has lost count of how many microcars he owns. “I’m always fixing them,” he said, and “they’re fragile and easily broken.” He added, “Every drive is a race to keep up with traffic.” When they work, however, it gives Mr. Hatten a “hit rush of satisfaction.” Microcars are the stars of his You Tube channel — he has his 11 Subaru 360 Super Deluxe cars and a 1962 Messerschmitt KR200 with a bubble top. “I like making people’s heads explode, then drive away,” he said. They are not for the faint of heart, and it helps if you’re good with a wrench.

They’re underpowered, noisy and sometimes smoky, and they may not have heat or wipers. “The struggle is what makes it fun,” Mr. Hatten said. He is quick to tip his hat to other devotees, too, including personal collectors or those with significant collections. Charles Gould and his Matchbox Motors Microcar, Minicar & Motorcycle Museum in Massachusetts and the Midwest Micro Car Museum in Wisconsin have helped pave the way for many microcar enthusiasts.

In Battleground, Wash., Damian Donesky, 38, restored a 1958 BMW Isetta microcar passed down within his family from his great-grandparents. His tiny transporter, Constanteeny, was nicknamed after his great-grandfather, Constantine. The Isetta has been in the family since the early ’60s. Mr. Donesky, a product designer for Rough Country, which makes aftermarket products for trucks and Jeeps, called himself a longtime “car nerd.” Mr. Donesky became a mechanic and has preserved his family’s automotive treasures. “I have three cars from the family,” he said — “my dad’s 1952 Willys M38 Army jeep, my great-grandparents’ BMW Isetta and BMW 700.” As a child I used to play on the Isetta outside my great-grandparents’ house.

I always loved that car, but never really thought I would own it.” His great-uncle passed the Isetta to Mr. Donesky. In 2020, during the pandemic, Mr. Donesky had months of leave for his first child’s birth. He started a restoration project, enlisting help from the Isetta Owners Club of Great Britain and Isettas R Us. Mr. Donesky did the bulk of the drivetrain assembly on the kitchen counter. “My wife didn’t want me out in the shop all day after the birth of our first baby and suggested I come inside and work on it,” he said.

The car was ready in 2022. The Isetta has one notably quirky feature: Its one door is at the front. That’s not all that’s unusual. “It shifts with the left hand,” Mr. Donesky said, “the shift pattern is...