If you mean the "Distributor" Name,I have no Idea what is the Difference.
Also these are "free" and "maybe" not legal Downloads....maybe Warez ?
(..please be so kind and refer to the GBAtemp Rules about the Term "Warez").
If you want to get it from Steam,there are no different Versions.
if you don't want to pay, get the mod version from moddb, if you want the full game, buy it on steam. the devs actually deserve the money, it's an amazing remake
EDIT: the moddb version is basically the full game, you just don't get the xen levels at the end. plus it's a bit outdated so you don't get a lot of the graphic overhauls the steam version got over time