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* When the developer only has a binary to work with (and not the [[source code]]), they recreate the engine rather than port it, hence the term '''[[wikipedia:Game engine recreation|game engine recreations]]''' (or alternatively '''game engine re-implementations'''). How the developers go about this process depends on their philosophy; they may opt to de-compile the original executable and have their own program rely on the original until all of its functions have been remade, at which point the original binary is no longer needed. Alternatively, they can be remade based on a clean room design, in which the project implements the abstract features without having to disassemble the original, going by how components are expected to be used rather than how the game uses them. Some engines come about simply because they were inspired by the original game, and the programmer felt confident enough that no reverse engineering was necessary to make an engine that does the same thing.

Some projects are implemented in ways that the original developer did not intend; for example, for a platform other than which publishers marketed it for. And they're not just limited to game engines either; [https://webamp.org/ Webamp] is a JavaScript application that re-implements Winamp in the web browser. These projects are almost always open-source, which also allows new programmers to fix bugs that could have been difficult to track down during development (alternatively, the bugs may be emulated to allow old mods to continue to safely exploit them). When most of the effort is on programming, the project will usually require the original game's assets (such as files in the installation directory or ROMs) until those ever get remade. This lets the developers claim they aren't infringing the game's copyrights since the player must obtain the original to use it; if the game is still being sold, this could allow the publisher to even earn revenue from the project. This aspect is debatable however, as some source code recreations did result in cease-and-desist letters and even lawsuits from companies such as in the case of [[re3|re3]] and reVC for the 3D-era ''Grand Theft Auto'' games, with Take-Two Interactive alleging that the source ports were made to facilitate piracy and that "the work is not licensed in any way"; some have speculated that the suit among others was to keep fan-made mods from getting in the way of their much-maligned ''Definitive Edition'' remasters.

|{{✗}}<ref group="N">XL Engine has ceased development, and has been superseded by [https://theforceengine.github.io/ The Force Engine] from the same developer</ref>

|Star Wars: Dark Forces, Daggerfall<br />''Later:'' Outlaws, Blood, Shadow Warrior

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|Zelda3

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|The Legend of Zelda: A Link to the Past

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|Blake Stone: Aliens of Gold, Blake Stone: Planet Strike

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|[http://www.descent2.de D2X-XL]<br />[https://www.dxx-rebirth.com DXX-Rebirth]

|{{~}}<ref group="N">PrBoom-plus is still active</ref>

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|[https://code.google.com/archive/p/quake-gamecube/ Quake GameCube]/[https://wiibrew.org/wiki/QuakeGX QuakeGX]<ref group="N">QuakeGX is a Wii port of Peter Mackay's GameCube Quake port. Both are available on the same website. A forked version of QuakeGX called [https://wiibrew.org/wiki/Quake_Wii Quake Wii] was later merged with QuakeGX.</ref>