To my mind, this game deserves more attention, because it is very interesting for several reasons. First, it seems to have been from the start developed with a great emphasis on openness and moddability, which eventually resulted in the game being open sourced.
The first public release seems to be v0.32 beta for Linux and SGI IRIX on Aug 28, 1995 (announcement), followed by v0.33 for DOS on Aug 31, 1995. These releases were under a shareware license and included a tutorial and the first four levels of the game. What is more, the developers, Crack dot Com, included a built-in level editor, and encouraged the players not only to create and distribute custom levels for the game, but to submit their work for evaluation to the developers, with the possibility of the levels getting commercially published (the terms of distribution for user-made levels are outlined in the included GAMEDEV.TXT). This attitude is quite unusual, since most shareware developers would actually expressly forbid any distribution of custom levels or mods designed to work with the unregistered shareware releases of their titles, as such unauthorized add-ons would increase the replay value of the free portion of the game, potentially reducing the incentive to buy the registered version.
Secondly, a significant portion of the game was written in Lisp, allowing for a great degree of customization. Players could create and easily launch their own mods, either on their own or as a part of a level pack. Many of the game's options are also changeable via the LSP files, e.g. it is possible to remap control keys by editing LISP\INPUT.LSP, and change some options like switching to the newly picked weapon in OPTIONS.LSP.
The developers also played around with high-resolution modes. In the DOS version, depending on the system configuration, the game can run in up to 1600x1200 resolution, as well as several non-4:3 ratio modes. This feature was eventually reserved for the built-in level editor only, as higher resolutions prove game breaking by revealing more parts of the level to the player, but DOS v1.05 and below can be run in high resolutions with the command line parameter -size x y or with -size ?, which will display a selection of available graphics modes. Here's a shot of v1.05 in 640x480:
Additionally, there is a "doubled pixels" mode which is closer to the original screen proportions (although it does not keep the aspect ration of the standard VGA mode):
This mode is activated with the parameters -2 -size x y.
A list of currently known shareware releases of Abuse can be found here. Version 2.00 is a shareware demo distributed by ORIGIN Systems/Electronic Arts. It has only three levels and a tutorial, as opposed to the earlier shareware releases, and the editor is disabled. However, this version is still capable of running custom levels and mods.
Soon after the release of the first shareware versions, some of the users took to creating new levels for the game. This FAQ mentions three single-player levels and a mod, created with v0.33. The community site www.abuse2.com (Wayback Machine copy) mentions quite a few levels, none of which seem to have been preserved by the Wayback Machine.
Another fan site however was archived with downloadable files: http://games.3dreview.com/abuse/index.html
The levels section includes some of the early levels dating back to v0.33 beta.
What is interesting though is that the shareware versions, including the more limited ORIGIN/EA one, are capable of loading and running even those levels that are explicitly marked as designed for the registered/commercial version of the game. It seems that the shareware version may replace missing registered assets (like registered-only weapon pickups) with shareware ones.
Source code release
On July 12, 1997, Crack dot Com released the source code of the game.
Source: official press release (Wayback Machine copy).The Abuse engine, although almost two years old- an "ancient game" in this
industry- still contains some features that many games today have not
implemented, including a built-in LISP engine, a joinable peer-to-
peer network architecture, portability to multiple operating systems,
support for multiple screen resolutions, and an extremely advanced built-in
editor with a portable window system.
In addition to the source, all shareware assets (excluding music and sound effects owned by Bobby Prince) were released into public domain. However, the registered version levels and data remained proprietary as EA, Bungie and other publishers were still selling the commercial versions of Abuse at the time. The title also remained copyright of Jonathan Clark and Dave Taylor. More info on the game's legal status can be found here.
Open source version
With the source code and a substantial portion of game data available, the community set on to create a free full game in what could be the first ever free game content replacement project. The game was called fRaBs, which stands for Free Abuse. Because a title containing the word Abuse would violate the clause of the source code license which forbids the use of the copyrighted original title of the game, this acronym was used instead.
Crack dot Com endorsed the project and for some time hosted fRaBs pages on their website, with a mirror maintained by Jonathan Clark on his personal site (these pages weren't preserved by the Wayback Machine though). fRaBs replaces registered levels with community created works, and also adds a number of user-made modifications. The latest DOS build is v2.10, available from the archived website of the project, or right here at dosgames.com.
The source code was also used to create a Windows port of the game, which was accomplished by Jeremy Scott. For this project, Jonathan Clark and Dave Taylor have apparently allowed to distribute the registered data set, according to the readme. The files are currently available from SourceForge and other places. Jeremy Scott also worked on an enhanced Windows version called Abuse 2, but this project was apparently never completed.
Abuse-SDL is a Linux port using the Simple DirectMedia Layer. This is probably the only related project still online. It also includes the registered data set, although the licensing is unclear. Earlier versions (Wayback Machine copy) just offered a copy of the files from Jeremy Scott's port, including the readme with the reference to Jonathan Clark's and Dave Taylor's permission, as a separate download. The latest release has apparently merged the engine, the registered data, and the fRaBs data into a single download.
iPhone version controversy
In 2009 a third party created a port of the registered version to iPhone, which was launched commercially on iTunes, without knowledge or approval from Dave Taylor. The entire story can be found in his blog.