In London, they are registered with Transport for London as a minicab company. Taxi drivers are unhappy with them their because only taxi companies are allowed to have meters. Minicabs (a cheaper licence) are supposed to quote the price of the journey in advance and charge that amount regardless of how long it takes them.
Addison Lee, the largest minicab company in London, has an app that is a bit like Uber's. However the difference is that when you enter the details of where you are, and where you want to go, it shows you the price of the journey on the screen, and if you press the "accept" button, that is what you will get charged. They generally seem to be cheaper than Uber and get you to your destination quicker.