Citing from the proj.4 home page,
proj.4 is a standard Unix filter function which converts geographic longitude and latitude coordinates into cartesian coordinates (and vice versa), and it is a C API for software developers to include coordinate transformation in their own software.My colleague Kristian Evers and I are currently working hard towards a goal of improving the proj.4 functionality for handling full 3D geodetic data.
Currently, my primary task is in implementing transformation pipelines in proj.4.
As a first proof-of-concept, I have implemented a tool called tran, which works somewhat like proj, but handles 3D data, and supports transformation pipelines.
Read the preliminary tran user's guide here
If you accept the licence (which disclaims all liability, in other words: You are on your own, the liability is yours, and the software may do anything, including eating your kids, burning down your house, and stealing your car), then you may download a recent Windows build of tran here
If you would rather build the software yourself, then take a look at my proj.4 fork over at GitHub
Or you can participate in the discussion over at the proj.4 pull request GitHub page.