Update: The creation of ReWired was made possible via the level editor, Deck, created by System Shock scholar Dertseha. They spent years (much of it without access to source code) reverse-engineering the game as part of their InkyBlackness project to create a comprehensive set of tools for the game.
Here's just what the horrifying cyborg doctor ordered to keep System Shock fans busy while we're waiting on the delayed remake and mysterious sequel. The original System Shock launched over 24 years ago, but only now are fans finally equipped with the tools to produce mods for the game, thanks to Nightdive Studios releasing the source code. System Shock: ReWired from old-school modder 3RDplayer is its first fan-made campaign, set aboard a medical ship - the UNN Bismarck - which has fallen under SHODAN's control.
While not as sprawling as Citadel Station, the Bismarck isn't a small ship. The campaign is set across three large decks, with four cyberspace layers connecting them and their many systems. As per Shock standard, you'll be following the story through scribbled notes, emails from crew and antagonists, plus the occasional audio-log left behind by the now mostly mutated or repurposed crew. Sadly there's no voice acting, so you'll need to turn on subtitles, but this does reduce the mod down to a minuscule ~250 kilobyte download.
While I've only had a chance to play a little bit of ReWired, it feels just like more System Shock. Kinda weird to be exploring all new corridors in such a familiar old game after nearly a quarter-century. While I've not yet made it off the Medical deck, it does feel somewhat more cramped and claustrophobic than Citadel Station, and ramps up the difficulty faster. Fortunately, health items seem to be quite generously distributed but ammo is scarce so be ready to bludgeon the occasional mutant with your trusty metal pipe.
Installation of the mod is admittedly a little more complex than with newer games, but not by much. You can find full installation instructions here, which require you to back up and overwrite a few files. With any luck, the next big System Shock mod won't be nearly as long in the making, thanks to a cross-platform source-port named Shockolate, currently in development. While it aims to provide as authentic a System Shock experience as possible, the developers do promise some quality of life improvements, including integrated mod support.