Tor (The Onion Router) allows to ensure anonimity using Onion Router, a node of the TOR network.
So the internet traffic isn’t routed in the traditional client – server way but uses a complex and crypto virtual circuit created with many Onion Router.
Sure you have heard about Dark Web, the “dark” side of Internet where is possible to find non indexed content (eg. cryptomoney services, hacking services and groups, etc…) and you can access it only with specific software, like Tor.
You can download Tor for various platforms: Windows, OS X and Linux, the mobile world isn’t excluded.
Android users can download Orbot and Orfox from Google Play Store.
The first allows to establish a connection to the Tor network, the second is a lightweight browser that uses Tor.
Orbot has an interesting feature: you can enable your installed apps (eg. Facebook, Instagram etc…) to use Tor with the big advantage to be anonymous not only for the web surfing.
An official Tor version for iOS isn’t available but many developers have made various Tor enabled browsers, you can find them on the App Store, like Onion Browser.