Maybe it’s the sudden flurry of flying car proposals or the hype over hyperloop, but it seems like tech companies are finally ready to build the cities of the future we’ve been obsessing about in films for years.

Smart city technology, a combination of Internet of Things connectivity and massive technological integration at the metro level, has long been a buzzy phrase for planners and designers looking to make cities smarter, more efficient, and more sustainable.

And cities have bought in: By 2020, the market for this new urban technology is expected to reach $34.4 billion annually, according to the Consumer Technology Association.

Of course, much of this development—from Kansas City’s progressive transit corridor to Columbus, Ohio’s proposal to create a smart, equitable transit (the winning entry in the U.S. government’s Smart City Challenge contest last year)—is finding clever ways to add this new technology to our pre-existing urban environment. China alone has more than 200 smart city projects in the works, and cities from Dallas to Amsterdam are proposing their own smart city districts.

But what about the truly mad scientists, the ones who want to start from scratch and reach for utopia? Lately, it seems many tech leaders have decided to take the challenge, offering their visions (or at least allocating funding) to see if they can realize these new visions of urban living.

Here are some of the most high-profile—and fantastical—examples of high-tech cities currently in some stage of planning or development.

Sidewalk Labs’ Urban Innovation Lab in Toronto

Announced last month with great fanfare, Sidewalk Labs’s plan to partner with developers on a prime, 800-acre site on the Toronto lakefront has been the most anticipated announcement of its kind.

The urban innovation company at the center of the new high-tech urban neighborhood, a unit of Alphabet, Google’s parent company, has already rolled out Wi-Fi hubs in New York City and a transit planning tool, but this project on the Eastern Waterfront will offer them a much bigger sandbox for experimentation and development.

The company will start with a $50 million investment in testing smart city tech, and suggested the future neighborhood will be "climate positive"—i.e. emissions will be net zero—with one in five housing units designated as affordable.

Most overwrought description: “We have an opportunity to fundamentally redefine what urban life can be.”

Score on Syd Mead scale: 4. Considering the Alphabet-associated company can benefit from the synergy of driverless technology, courtesy of Waymo, and vast troves of Google and Google Maps data, this seems both the most reasonable proposal, and the one with the most chance of popularizing big ideas.

Bill Gates’s Desert Metropolis in Belmont, Arizona

Set to be as large as Tempe, Arizona, this proposed built-from-scratch smart city, located on 24,800 acres west of Phoenix, is backed by a cadre of investors including Microsoft co-founder Bill Gates.

The billionaire hasn’t come out and directly noted his involvement, but since his Cascade Investment LLC controls Belmont Partners, the real estate investment group planning to pump at least $80 million into the proposal, it’s safe to assume he’s involved on some level.

The new metropolis will include 80,000 homes, 3,400 acres of commercial, office, and retail space, and 470 acres set aside for public schools. But, more importantly to building high-tech hype, it will also feature autonomous fleets (Arizona’s laws are very welcoming for driverless car trials), autonomous logistics hubs, high-speed digital networks, and “new manufacturing and distribution paradigms.”

Most overwrought description: “Belmont illustrates that Arizona remains at the leading edge of trends in American urban planning and development keying off of advances in solar power and electric distribution systems, autonomous auto testing, broadband, and data centers.”

Score on Syd Mead scale (0-5): This rates a 1. Many of the technologies under discussion, such as solar power and broadband, should be contemporary at this point, not futuristic. As Henry Grabar argues in Slate, it may actually just be a development taking advantage of a forthcoming highway project, a form of “smart” development that’s been around for decades.

NEOM, the Saudi Arabian Crown Prince’s Pet Project

As the traditional oil power transitions to a more diverse, tech-based economy, it seems natural to look at splashy innovation hubs and tech centers as key parts of the shift.

Of course, considering the wealth of the Saudi royal family, an entire city seems more fitting. NEOM, the brainchild of Crown Prince Mohammed bin Salman, would be a $500 billion high-tech development along the country’s Red Sea coast, reportedly taking up more than 10,000 square miles.

Expected to open by 2025, the “technology-forward development” and app-driven city, funded by sale of stock in the state-run oil business, will seek to incorporate artificial intelligence and the Internet of Things, and has reportedly reached out to e-commerce giants Amazon and Alibaba to see if they’re interested in setting up shop.

What’s crazier is that this is perhaps one of the less ambitious schemes being undertaken in Saudi Arabia. In addition to building the city of the future, the country wants to turn an area larger than Belgium into a tourist destination (it’s set to break ground in 2019) and build a city called Al Faisaliyah, set to be larger than Moscow.

Most overwrought description: “A startup the size of a country that will change the way we live and work forever.”

Score on Syd Mead scale (0-5): Four, though hopefully it won’t end up like Bladerunner 2049-era Las Vegas.

Y Combinator’s New Cities Initiative

While this research project by one of Silicon Valley’s most famous tech incubators hasn’t purchased real estate or broken ground yet, it’s captured a lot of people’s imagination. With experience turning tech ideas into big-name companies such as Dropbox, it’s no surprise some see Y Combinator as a potential hotbed of urban innovation. And, to be fair, they clearly said they’re not interested in “crazy libertarian utopias for techies.”

Most overwrought description: “Our goal is to design the best possible city given the constraints of existing laws.”

Score on Syd Mead scale: 3. It’s still in the nascent planning stages, but who knows where Silicon Valley talent and funding could go?

Seasteading Institute’s Floating Cities in French Polynesia

And then, there’s the more eclectic Silicon Valley visions of the future. Backed by both Peter Thiel and led by an actual person named Joe Quirk, the Seasteading Institute, a San Francisco non-profit, seeks to create island cities in French Polynesia.

According to a recent New York Times article, the group plans to starting building out floating structures and have a dozen operating by 2020. While the plans so far don’t necessarily include the high-tech gadgetry of other projects, the concept does push progressive ideas of sustainability, including living roofs, coconut fiber construction, and recycled materials. And it’s not hard to imagine a project backed by tech titans wouldn’t feature some advanced technology at its core.

Most overwrought description: The title of this piece on the movement says it all: “Seasteading: How Floating Nations Will Restore The Environment, Enrich The Poor, Cure The Sick and Liberate Humanity From Politicians.”

Score on Syd Mead scale: Full 5, approaching Waterworld.

YarraBend, the Tesla Town of the Future

How could we possibly get through this without mentioning Elon Musk (and no, we’re not talking about Mars)? In Australia, a small suburb outside of Melbourne is under construction that features homes kitted out like Tesla showrooms, with the company’s rooftop solar and battery storage systems, as well as electric car recharging stations, and energy efficient lighting. Local developer Glenvill says people will move in over the next few years. Like other sustainable tech-led developments, such as Panasonic’s plans in Denver, the small community may provide blueprints for bigger projects down the road.

Most overwrought description: “We’ve actually never seen anything like this in the world.”

Score on Syd Mead scale: 3. It’s no hyperloop, but Tesla’s sustainability technology, which can make buildings of any size operate with a more intelligent and green energy system, offers a decentralized, small-scale view of future urbanism.