Availability is genuinely country-by-country. Uber operates in a large share of the world but is absent, banned, or merged into local players in plenty of markets: Southeast Asia belongs to Grab, China to DiDi, much of Eastern Europe and Africa to Bolt, India splits between Uber and Ola, and several countries run strong homegrown apps or route everything through licensed taxi apps instead. A few places restrict ride-hailing entirely, leaving taxis as the only legal option.
The pre-trip homework takes ten minutes and pays off the moment you land: search which app dominates your destination, install it, and register at home while SMS verification and card setup are easy, since some apps are temperamental about foreign numbers and cards.
On safety, the mainstream apps carry a similar toolkit now, driver identity and ratings, plate matching, live trip sharing, in-app emergency buttons, and anonymized calls. Coverage and reliability are strongest in major cities and thin out in small towns and late at night, so keep the local taxi option in reserve. Where an app operates legally and shows plenty of cars on the map, it is typically as safe as, and more transparent than, hailing on the street.