OnionCat is described as 'creates a transparent IPv6 layer on top of TOR's hidden services. It allows users to anonymously access Internet services. It transmits any kind of IPv6-based data transparently through the TOR network on a location hidden basis' and is an app in the Security & Privacy category. There are more than 10 alternatives to OnionCat for a variety of platforms, including Mac, Linux, Windows, Android and BSD. The best alternative is Tor Browser, which is both free and Open Source. Other great apps like OnionCat are Tor (Free, Open Source), Freenet (Free, Open Source), I2P (Free, Open Source) and GNUnet (Free, Open Source).
The Tor software protects you by bouncing your communications around a distributed network of relays run by volunteers all around the world: it prevents somebody watching your Internet connection from learning what sites you visit, it prevents the sites you visit from learning...
Tor is free software and an open network that helps you defend against traffic analysis, a form of network surveillance that threatens personal freedom and privacy, confidential business activities and relationships, and state security.
GNUnet is a framework for secure peer-to-peer networking that does not use any centralized or otherwise trusted services. A first service implemented on top of the networking layer allows anonymous censorship-resistant file-sharing.
Bitmask is an EXPERIMENTAL open source application to provide easy and secure encrypted communication. You can choose among several different service providers or start your own. Currently, it supports encrypted internet (VPN) and encrypted email.