HDF5 can be built using two build systems: the Autotools (since HDF5 1.0) and CMake (since HDF5 1.8.5). For a long time, the Autotools were better maintained and CMake was more of an “alternative” build system that we primarily used for handling Windows support (the legacy Visual Studio projects were removed in HDF5 1.8.11).
This is no longer the case though—CMake support in HDF5 is (almost) as good as Autotools support and CMake, in general, is much more commonly used now than when we first introduced it.
So why are we still hanging on to the legacy Autotools?