A new tool for hdf file conversions.
Quite a few times I've been annoyed and/or frustrated by the incompatibility of hdf4 and hdf5 file formats. For more info, see the HDF Group. Generally they do a good job, and the backwards-compatibility breaking was necessary, but it's still annoying.
In particular their conversion tools don't have binaries available for OS X (what I use, mostly), and compiling them is a bit of a pain. Further, the Ubuntu packaged tools also seem to be pretty buggy. So what I've done is write a simple web wrapper around the HDF tools using the fantastic jQuery file upload library.
The page is hosted at hdf.azylstra.net and currently supports uploads up to 50MB.