http://www.malfador.com/se4mods.html has it all.
P&N = Pirates and Nomads
TDM = a "mod" that is really a collection of a bunch of custom tweaked AIs, that provides much stronger AI opponents than the stock game does.
PBW = Play By Web, a server that automates the hosting necessities of hosting a PBEM (Play By Email) multiplayer game
AIC = AI Campaign, which is loosely based on Proportions and has a lot of custom techs and comps for AIs to get around as many of the limitations of the AI as could be done, without much in the way of just giving them superstrong weapons/shields/etc.
[ December 11, 2003, 23:42: Message edited by: Imperator Fyron ]