.FMXLIST file
From Fmepedia
.FMXLIST is the file extension for an FME Transformer Category.
Double-clicking a .fmxlist file causes it to be installed to <my documents>/FME/TransformerCategories - if the file is already installed then you are given the option to over-write the existing file, install the new file under a new name, or not to install at all.
