TopMod is a topological mesh modeling software that allows you to create 2-manifold meshes. It is portable and using this you can create amazing shapes and even remesh shapes and do a lot of other interesting things. It lets you add or delete meshes so that you can create or delete handles or open/ close holes or connect/ disconnect meshes. These operations are consistent with subdivision algorithms.
In particular, these operations can easily be included into a subdivision modeling system such that the topological changes and subdivision operations can be performed alternatively during model construction.