Quote - It's the D|S SDK, as in Software Developement Kit.

It gives you access to the internals and code that runs D|S so that you can write plugins for D|S. Like eg if you wanted you could code a plugin that recreates the flocking behavior of birds and add it to D|S. The SDK would give you a library of functions to read various parts of the D|S scene, change it to your needs and finally send it back to the scene. And if you thought it would be a popular tool, you could also sell it.

I wish poser had something similar.

Python should give you access to all those things, and you can combine it with ordinary C/C++ code (PoserPhysics is one plugin that does that). Do you have something specific in mind? If you want to do something that's not available from Python, make sure to send a feature request to e frontier.