The beauty of the Psiphon system lies in the fact that it utilizes multiple transport systems, so that if one protocol is blocked by a censor, users can switch to an alternative mechanism. If a user encounters a block when using VPN, for example, he or she can switch to SSH or obfuscated SSH (SSH+) instead (at least in theory).
Psiphon is a powerful tool which is designed to evade internet censorship. Developed and maintained by Psiphon Inc. (although originally written by researchers at Citizen lab on behalf of the OpenNet Initiative (ONI)), it uses a combination of VPN, SSH and HTTP Proxy secure communication and obfuscation technologies to bypass the kinds of internet filtering (i.e. Censorship) systems commonly used governments.