Shrak is an unofficial total conversion mod developed for id Software's Quake by Quantum Axcess. Released January 30, 1997 at an MSRP of $19.99, it received modest success and provided the financial shot in the arm necessary for Quantum Axcess to develop the significantly more popular and highly regarded Malice.
Shrak's environments tend to be more abandoned-looking than Quake's, with a greater emphasis on post-apocalyptic themes and puzzles. The provided Red Book Audio soundtrack is ambient electronica by Bonetribe. It shipped with Capture the Flag, Deathmatch, and Bugwar game modes, the latter of which allows the player to compete in teams of either scorpions or spiders.
Matt Walsh made all of the Quake-C programming changes consisting of a combination of original code and ideas submitted/borrowed from other Quake-C authors. He discovered id's original code that checked whether the player was in the water dominated the performance profile. He changed the code so this expensive check was made half the time, causing this routine to disappear from the profiling data completely with no perceptible changes. Walsh also fixed a few bugs id had left in, such as some of the code to play the unlocking sound for certain doors.
Code for the Shrak monster itself was a bit tricky. Shrak is killed in 2 stages. The first stage is basic; hit Shrak with enough damage from any angle until he splits open revealing his heart. But then his heart must be hit directly with the inflator gun. The geometrical calculations to determine if this had happened were not straightforward, because bounding boxes in Quake translate but do not rotate — the rotation of characters is strictly an aesthetic feature. This was one of the first FPS implementations of a character that reacts differently to attacks based on the point of impact.
Nearly every sound was re-engineered in Shrak. Many of them were done by Walsh, inspired by the 'shaped raw sound' techniques used by sound engineers of early sci-fi movies such as Star Wars. One of the most useful techniques discovered was to reduce the speed of the sound. Attentive players will notice that they can hear "When Twilight Falls on NGC 891" by Martin Segundo and his Scintilla Strings as performed in the movie Dark Star. The last 4 notes of "When the Levee Breaks" as performed by Walsh on keyboard can also be discerned when picking up certain weapons.
The structure of a Quake map (or BSP) is such that all texture resources for that level are contained in a WAD2 file (to prevent confusion with Doom's WAD file format). Consequently, any levels made with the original Quake's textures contain id Software's intellectual property. These could not be distributed without id's consent and compensation. Because Quantum Axcess was unwilling or unable to pay id Software for the rights to use its textures within the levels, they came up with a workaround: Shrak's maps contain none of id's intellectual property, but an application included on the CD-ROM processes Shrak's PAK files and adds id's textures to them, and exploits this legal loophole. Following Malice's release, id Software changed Quake's licensing structure to prevent this from happening. Impel Production's unofficial third mission pack, Abyss of Pandemonium shows the results of this: all textures are cleverly designed lookalikes to avoid potential legal liability.
The provided third-party texture combining application does not work outside of Windows 95, 98, or Millennium Edition, or a DOS-compatible environment. Linux users have presumably been out of luck since the beginning, and Windows NT 4.0/2000/XP users are unable to play the game without going to some trouble. One workaround for this is to create a small partition on a hard drive, install Quake to it, boot the PC from a custom boot disk with a DOS install and CD-ROM support, install Shrak, and then recopy these files to the volume where Quake is installed. It is also possible to use DOSBox to run the executable from the command-line.
There is also an updated version of the combining application available on the FAQ page of the Shrak homepage, along with instructions for completing the installation.