Here are some educational resources/explanations for the games community about emulation and other game-related tools.
Note: Check my top-level replies in this thread as I ran out of text in the post
[Informational Resources]
Reddit's ROM Megathread - Unaffiliated with this site
[Emulation as a field]
Emulation is the process of re-implementing the functionality of something (hardware and/or software) in a separate software environment. You're probably most most familiar in the term as it relates to game system emulation- like the Dolphin Wii and Gamecube emulator, but it's actually much broader than that.
While emulation does cover physical systems, it can also cover things that strictly exist as software. If you've ever played on WoW or any other MMO private servers, the actual underlying software that was being run was likely a server emulator (or in rare cases the actual official server software itself may have leaked or released).
These server emulators are created by analyzing the network information exchange (packets) sent from the game client to the server and those received by the client from the server. A painstaking and brutal process of analyzing these packets allows server reverse-engineering projects to then re-implement the functionality of the official servers, and then we can point the game client towards our reverse-engineered private server (that speaks the exact same "language" as the official servers). This then allows the private servers to provide additional or changed functionality (for example, more exp per quest) which allows a much more customizable experience.
Emulation can also be used to re-implement vendor solutions like the Steam API which provides various utilities like DRM (which the emulator could choose to ignore). A great example of an emulator in this regard is the Goldberg Emulator.
Let's say you've acquired (through legal purchase only of course) the clean steam files for a game and want to run it offline. Normally you wouldn't be able to because the steamworks DRM check wouldn't be able to authenticate against the official steam servers. If we instead replace the steam_api.dll (this could also be named steam_api64.dll depending on the game) with the one provided by the Goldberg Emulator, when the game makes the check for the steamworks drm authentication status, the Goldberg Emulator's implementation of steam_api.dll will simply return true and let us play our game offline. The game itself just knows that it asked for a DRM verification check to a service, and the Goldberg variant of steam_api.dll looks (to the game) exactly like the "real" version, except that it always returns that the steamworks DRM has been verified.
Refer to the readme within the Goldberg project for more information about what to do with specific games. Also take note that this only works with games that only use steamworks drm (most of them) and games using other/multiple DRM solutions won't work with this method only for offline play.
[Console Emulators]
All of the emulators listed below are my personal per-console pick. Each is at least in the recommended section of a great general emulation resource, the Emulation Wiki
Game Platform | Emulator Name | Emulation Platform | Comments
Nintendo Consoles
NES | Ares | Windows/Linux/Mac
SNES | Ares | Windows/Linux/Mac
SNES | bsnes-hd | Windows/Linux/Mac | Widescreen modifications for some SNES games
N64 | Simple64 | Windows/Linux | N64 emulation has a lot of viable candidate emulators, check the page here
GC | Dolphin | Windows/Linux/Mac/Android
Wii | Dolphin | Windows/Linux/Mac/Android
Wii U | Cemu | Windows/Linux
Switch | Ryujinx | Killed by Nintendo 10/1/2024
Switch | Yuzu | Windows/Linux/Android | Killed by Nintendo 3/4/2024
Nintendo Handhelds
GB/C | mGBA | Windows/Linux/Mac
GBA | mGBA | Windows/Linux/Mac
DS | MelonDS | Windows/Linux/Mac/Android
3DS | Citra (PabloMK7 Fork) | Windows/Linux/Mac/Android | UPDATE 10/31/2024 Pablomk7 will be joining efforts with Lime3DS on a new project in the near future
Sony Consoles
Playstation | DuckStation | Windows/Linux/Mac/Android
Playstation 2 | PCSX2 | Windows/Linux/Mac
Playstation 3 | RPCS3 | Windows/Linux/Mac
Playstation 4 | ShadPS4 | Windows/Linux/Mac | Heavily experimental and not for casual use yet
Sony Handhelds
PSP | PPSSPP | Windows/Linux/Mac/Android
PSVita | Vita3K | Windows/Linux/Mac
Sega Consoles
Sega Master System | Ares | Windows/Linux/Mac
Genesis | Ares | Windows/Linux/Mac
Saturn | Mednafen | Windows/Linux
Dreamcast | Flycast | Windows/Linux/Mac/Android
Microsoft Consoles
Xbox | Xemu | Windows/Linux/Mac
Xbox 360 | Xenia | Windows
Apple Phones
iOS 2.x | TouchHLE | Windows/Mac/Android
[Graphics Packs]
A lot of emulators have texture replacement capabilities built into them. What this means is that users can manually and/or AI upscale textures from the game into higher resolution or outright replace them with other textures. There aren't currently (that I'm aware of) area that have consolidated links to these things, so you'll unfortunately have to search individual project forums and look for texture or graphic packs links.
Some known graphics packs repositories:
Citra Forums Killed by Nintendo 3/4/2024; waiting for the dust to settle for recommendations
[Graphics API Translation Layers]
Sometimes there are scenarios where a game may only use DirectX to draw it's rendered graphics to screen and we may not want this. This could be for performance reasons (maybe the Vulkan graphics api has better performance, maybe DirectX isn't available on our OS, or maybe the DirectX version is really old and not properly supported by our OS/GPU/Driver combination). In these instances we can use translations layers to translate DirectX graphics api calls into Vulkan calls using utilities like DXVK . Explaining which files to copy over depends on a per-DirectX version basis, so you'll have to use a combination of the PCGamingWiki and DXVK documentation to figure out which files to replace.
[Graphics Post-Processing]
With a utility called ReShade we're able to inject various post-processing effects into the final stage of the graphic rendering pipelines of games. This allows you to adjust color curves, inject path-traced global illumination (a method like ray-tracing), and add a bunch of other effects to DirectX9/11/12/Vulkan games.
[Engine Reimplementations]
This is a relatively new area that gaining a bunch of steam right now where people re-make the engines (the thing that actually runs a game) for older games in order to support newer hardware and vastly broaden the scope of modding functionality. Essentially what these projects do are take the assets from a game (textures, models, etc) and then load them into a a modernized game client (with all the bells and whistles you'd expect from a modern project in terms of graphics settings and compatibility). Most of these projects require a subset of the original game files to run, so make sure you acquire them prior to running these projects.
Projects
OpenMW - a Morrowind engine re-implementation
TES3MP - an OpenMW fork focused on multiplayer support
OpenRCT2 - a Rollercoaster Tycoon 1 and 2 engine reimplementation that greatly boosts compatibility, removes legacy game restrictions (park size, number of rides in park, number of decoration in park) as well as adding online multiplayer
OpenTTD - A Transport Tycoon Deluxe reimplementation that I'm not especially familiar with but I see get good mentions
[Game Decompilation Projects]
A more recent trend falls under the umbrella of game decompilation. The goals of these projects are to reverse-engineer games in a way that results in source code that when coupled with a games assets will produce a 1:1 exact replica of the ROM it was reverse-engineered from. Once this feat is accomplished (and more complex things like shiftability have been achieved) people can take the functioning source code and build around/on top of it to add new functionality, change existing functionality, and create native ports for various new platforms.
For more information, search around the internet for game decompilation projects and reference this thread as a decent starting point for tracking projects.
Some games with WIP or finished PC ports include:
The Legend of Zelda: A Link to the Past
The Legend of Zelda: Ocarina of Time
Super Mario 64
Jak and Daxter: The Precursor Legacy
Sonic Mania
Super Metroid
Super Mario World
[Notable Game Mods and Fan-Remakes]
PrimeHack - native mouse and keyboard controls for the Wii Metroid Prime Trilogy games. This is a Dolphin emulator fork.
AM2R - Another Metroid 2 Remake
DSP Nebula Mod - Multiplayer mod for Dyson Sphere Program
Nehrim - Mod using the Oblivion engine to build a unique fantasy story independent of the elder scrolls universe
Enderal - The sequel to Nehrim using the Skyrim engine to build a unique fantasy story independent of the elder scrolls universe and probably one of the best WRPGs of all time
Nitrox - Subnautica Multiplayer mod
Stardew Valley Expanded - an absurdly impressive mode for Stardew Valley that explodes the amount of content in the game
Space Exploration; Bob's mods; Angel's Mods - 3 separate incredible mods for Factorio