What about a website like Just Eat in the UK, which offers an online ordering interface to thousands of independently run takeaways in the UK, are they are technology company or a food company?
They're primarily a tech firm. Particular distinctions from Uber are: You know which restaurant you're ordering from, you sometimes pick it up from the restaurant itself. They never try to make it sound like they're the service; they're saying that they connect customers and businesses. The businesses stand up on their own; they're just brokering the deal.
The difference is that with UberX, Uber is the service from end to end; they perform every single role of the taxi firm; they tell the drivers where to go, they pay the drivers, etc.
Neither. I'd probably call that business services or retailer/reseller.
There's also the salient difference that those takeaways are not being paid as contractors by Just Eat (if anything it's probably the other way around). If they were, Just Eat would be a takeaway. If Just Eat made a piece of software for sale that other companies could use to provide takeaway resale services, it would be a technology company.