The HS Decompiler (HSDECMPL) is a tool written by TMC. It produces an HSS plotscript file out of a compiled .HS scripts file. It is for those people who have accidentally deleted or lost their original scripts, but still have their .RPG or .HS file.
For obsolete versions only: This utility is intended only for scripts compiled with HSpeak versions older than 3I (2009-07-27) -- that is the version which started to include a copy of the original scripts in the .HS file. However, a couple pre-3I features (mostly 'switch' and 'plotscript') are still not supported. They'll be added as they are requested/required.
As of version Dwimmercrafty, in the Script Management menu you will find a new Export scripts backup copy (.hss) option. If you're looking at a game made since 2009, this should export the real, original copy of the scripts. If you're looking at an older game and you're on Windows, Custom will automatically download and run HSDECMPL to produce an .hss file for you! Running HSDECMPL in this way rather than manually is highly recommended.
If you're using a different operating system, or it doesn't work, you can compile it yourself or email me for help.
(You don't need this; see above!)