Inferno Release 1 was one of the first campaigns released for Inferno (besides the Ancient Demos) and covered the war for Sol and the return of the Shivans.
Inferno Release 2 was cancelled, but have no fear, it was replaced by Inferno SCP, a new campaign which is a complete rework of Inferno, including a new Chapter 1 new weapons, ships, new AI, fighterbeams, etc. Its release however is long from now.
An earlier release is Inferno: Alliance, designed to be compatible with Inferno SCP, it covers what happend after Sol was cut off from the rest of the galaxy.
Other Inferno related campaigns are
Sol: A History, which is sort of like Alliance, but optimised by R1, created by Blaise Russel. There is also
Steadfast and Dreamcatcher.