Aristos
Lightseeker
There was none in the Civ4 so-called "SDK".
Civ5 SDK include some, like ModBuddy and much more importantly the FireTuner. The last one would have been very usefull for Civ4.
The source code is not a SDK, you need a compiler to be able to use it.
Ho, the current SDK is far for perfect, some of it's tools are broken since the beginning, others have been broken by patches, but it's here. And it's rightfully called "SDK". "Incomplete" is the word you're searching I think.
Now this is funny. We cannot even agree on which one has something closer to a real SDK...
Modbuddy an SDK??? maybe an MDK, as in Mod Dev Kit... but never part of an SDK. Firetuner, I don't know... debugger? but still, to me far away from being something close to an SDK...
Yes, source code still needs a compiler (and some knowledge), but it is to me far closer to an SDK than Modbuddy...