So, why is there no GNUber?

Most of what Stallman complains about would go away if there were no profit-seeking corporation sitting in the middle. If no one were trying to collect a 20% tax on taxis, you wouldn't need to pay with a credit card and you could have anonymous cash rides. Heck, without the need for a company to have something to take a 20% cut of, you could have actual ride-sharing.

A free, open-source app could be written and verified to not track its users, beyond the need to provide location services at the moment a call for a cab is placed.

So why haven't I ever heard of the free, open-sourced alternative to Uber & Lyft?