baseclasses contains, well, base classes that are used together with the rest of MDO lab tools.
It includes the various problems to be defined by the user in order to perform some analyses, such as
AeroProblemStructProblemAeroStructProblem
It also contains some class definitions shared by various solvers, such as AeroSolver.
Finally, it also contains a class, BaseRegTest, which is used as part of the testing toolchain.