TW - main game rules
TM - main construction rules
TO - advanced game rules and advanced support vehicle construction and equipment rules
SO - repair/refit rules, advanced space combat, quirks, frankenmech rules, Advanced space unit construction, Battleforce
IO - Advanced Mech construction, era specific unit construction, weapons and WMDs. Larger scale games
CO - design campaigns. Make forces. SPAs
AToW - main RPG rules
AToW Companion - more RPG options, and equipment for more eras
Battletech Manual - standard and some advanced rules geared towards mechs, latest quirks
ASCE - alpha strike rules