Roland
Yes, such a converter exists; it is part of the SimulationIO package <
https://github.com/eschnett/SimulationIO>, and is called "sio-convert-carpet-output". It should be built by the default makefile target.
You call it as "./sio-convert-carpet-output [--copy|--extlink]? <output file name> {<input file name>}*". There is one output file, and there can be multiple input files (e.g. one for each process). The "copy" option copies datasets, the "extlink" option creates external links to the original HDF5 files. The latter is faster and creates smaller files, but you obviously need to keep the originals around, and need to preserve their path (either their relative or absolute path, depending on what you specified on the command line).
I believe one of these two options is currently broken in the development version, sorry about this. I don't recall which.
-erik