Inferno Release 1 was the original Inferno. It was discontinued and redone in Inferno SCP.
Sol: A History is an (old?) mod by Blaise Russel telling what happened in Sol after the Great War. It is not by the Inferno team.
INF: A (Inferno: Alliance) is the canon (Inferno) version of what happened in Sol after the great war. It is by the Inferno team.
INF SCP is the new Work-In-Progress version of Inferno. it follows the same basic storyline of Inferno Release 1.
It will be released on December 12, 2012. INFA2 is the sequel to INF: A, following the rise of the Earth Alliance and the (Jovian War?).
INF: A Stand Alone is an upgraded version of INF: A with better graphics, missions and more ships. INFA2 will be released as a mod for INFASA.