The following emulators are common in speedrunning. Some communities may ban emulator speedrunning.

• GBA (& e-Readers)

• mGBA

• DS

• Desmume (recommended)
• melonDS

• Old PC games (Windows 95/98, XP, etc)

• Virtual Machine

• Mobile

• Bluestacks (For Android) (There are no known usable emulators for iOS)

• GB & GBC

• Gambatte (Recommended)

• Pokémon Mini

• PokéMini

• Emulator that some communities may not allow while some communities may allow.

• Yuzu (Switch)
• Dolphin (GameCube, Wii)

Sorry if there is any wrong information. This list will be update.

I have some update recommendations:

• MS-DOS

• DOSBox (& branches like DOSBox-X or DOSBox ECE)
• ScummVM (tbh deserves an own spot, cause afaik it doesn't only emulate DOS-games)

• SNES

• Snes9x

• Windows (for us linux users)

• Wine
• Proton via Steam

That's at least the stuff I know is used, but ofc there is a lot more especially for old consoles like C64, Amiga, PS, Atari, ...

More recommendations:

• PS1/PSX

• mednafen
• RetroArch (Beetle/Beetle HW cores)
• BizHawk v2.4.2/v2.5.2 onwards (though it has TAS capabilities, so bear in mind)
• DuckStation
• ePSXe v1.9.0 (this emulator in particular is kinda outdated, but most games still accept it)

-Sega Genesis/MegaDrive •Fusion •Genesis Plus GX

-Atari 2600 •MAME •Stella •Javatari

For games that allow it:

• PS2

• PCSX2 1.6.0

There are some emulators on phone and website (Java) and those emulators are generally not accepted.

Bizhawk, the amount of platform it covers and its accuracy is a safe bet.

Virtual Boy

• BizHawk Sega Pico
• Fusion/RetroArch NeoGeo Pocket
• RetroArch

feel like DuckStation should be on here for the PS1

I think a usable emulator for IOS is the Mac App Store if it has the game on there