Star Fleet Battles: Module C6 Lost Empires covers the extinct Paravian and Carnivon empires, presented as their ships and weapons would have been by the time of the General War (except for that annoying extinction thing). Each empire is presented with multiple alternate histories, although players can ignore both and write their own if they wish.
The Carnivons might have existed as a major empire between the Lyrans and Kzintis, or they might have escaped to the WYN Cluster.
The Paravians might have survived Gorn attempts to destroy their empire and could have ended up allied to the Romulans (while the Inter-Stellar Concordium became allies of the Gorns). Alternately, they could exist as edge-of-the-map raiders.
The rulebook includes the rules for playing the Carnivons and Paravians in the General War era, the empires that almost were. You will find the rules for heel nippers, deathbolts, and quantum wave torpedoes as well as 10 scenarios for you to play.
You will need the rulebook from the Star Fleet Battles Basic Set (or the Master Rulebook) to use this material. Access to Advanced Missions as well as Modules J, J2, K, and M (or the Master Rulebook) is needed to use the material to the fullest extent.