Well Conspiracies Part II was the sequel to Part I & II which has been released for OFP in 2004 and 2005.
Conspiracies Rising Dead was a standalone and has nothing to do with Part 1-3. The xDLC has to be played in the right order. So Maingame, Hidden Danger and Call of Prypjat.
Substance was an experiemental mod for our scripts.
Operation Evac also, but MP playable.
Apocalypse 1 & 2 also standalone and has to be played in the right order.
Conspiracies 4 is the official sequel to Part 1-3.

But the next Conspiracies will be something totally different. =) Let you surprise