Video game emulation is the general act of using a video game console emulator to play games, often packaged in a ROM or ISO file, that were released for certain console or handheld. It's usually done with computers, but people have tried doing it on other consoles and smartphones.

• Famicom / NES / Dendy:
  • FCE Ultra X (FCEUX) - The recommended NES emulator, which now supports bootlegs?!
  • Mesen - ?
  • Nestopia Plus! - Chinese fork of Nestopia. Scroll down for a Nestopia Plus thread.
• SuFami / SNES:
  • Snes9x - The recommended SNES emulator.
  • higan (bsnes) - An overpowered multi-console emulator. Not personally recommended.
  • ZSNES - An ancient emulator that hasn't been updated since 2007.
• N64:
  • Project64 - They replaced the PUP installer with Nagware, so see instructions here.
  • Mupen64Plus - A known alternative to Project64.
• GCN and Wii:
  • Dolphin - The only GameCube and Wii emulator out there.
  • Ishiiruka Dolphin - Dolphin fork. More friendly to low-end computers.

• GBC:
  • BGB - ?
  • Gambatte - ?
• GBC and GBA:
  • VisualBoyAdvance (VBA) - It's ancient, but still works. Latest: v1.7.2 and v1.8.0-β3.
    • VisualBoyAdvance-M (VBA-M) - VBA fork. Dead site, kinda alive, kinda bad…
  • mGBA - An entirely new GameBoy Advance emulator, but it's still in beta and may have issues.
  • No$GBA - This still exists and still has support for Nintendo DS games.
• NDS:
  • DeSmuME - They haven't made a stable release in years.
  • No$GBA - This still exists and still has support for Nintendo DS games.
• 3DS:
  • Citra - It's still in early development.

• Mega Drive / Genesis:
  • BlastEm
  • Kega Fusion
• PS2:
  • PCSX2 - And here's the BIOS.
• PSP:
  • PPSSPP
• PC-98:
  • Neko Project II - Ancient, still works.
    • Neko Project II (fmgen) - The fork made for Touhou Project.
    • Neko Project 21/W
  • Anex86
  • T98-Next

• [a] - Alternate version(s).
• [b] - Bad Dump. Avoid these if possible.
• [BF] - Bug Fix.
• [c] - Cracked.
• [f] - Other Fix. ROM has been altered, so it would run better.
• [h] - Hack. ROM has been modified in some way.
• [o] - Overdump. ROM has more data than there is. The extra information means nothing.
• [p] - Pirate.
• [t] - Trained. ROM has been modified with a cheats menu or something.
• [T] - Translation. ROM has been translated.
• [U] - ?
• [x] - Bad Checksum. ROM has a bad checksum.
• [!] - Verified Good Dump. ROM has been verified to work.
• ZZZ_ - Unclassified.
• (Unl) - Unlicensed. The game is probably pirated, unlicensed, or a bootleg.
• (???k) - ROM size.

• [C] - GameBoy Color.
• [S] - Super GameBoy.
• (M#) - Multilanguage. # = Number of languages.
• [M] - Mono only (NeoGeo Pocket).
• (PC10) - PlayChoice 10 (for NES).
• (1) - Japan (Genesis).
• (4) - USA (Genesis).
• (5) - NTSC Only (Genesis).
• (8) - PAL Only (Genesis).
• (BS) - BS ROMs (SNES). Read Satellaview.
• (ST) - Sufami Turbo (SNES). Read Sufami Turbo.
• (NP) - Nintendo Power (SNES). Read Nintendo Power (cartridge).
• (Adam) - ADAM Version (ColecoVision). Read Coleco Adam.
• (PAL) - PAL version.

• (A) - Australian.
• (C) - Chinese.
• (E) - Europe.
• (F) - French.
• (FN) - Finland.
• (G) - German.
• (GR) - Greece.
• (HK) - Hong Kong.
• (I) - Italian.
• (J) - Japan.
• (K) - Korean
• (NL) - Dutch
• (PD) - Public Domain
• (S) - Spanish
• (SW) - Sweden
• (U) - USA
• (UK) - England
• (Unk) - Unknown Country
• (-) - Unknown Country

• Emulation General Wiki - It's probably the best video game emulation resource.
  • ROM & ISO Sites