RetroArch is a frontend for emulators, game engines and media players.
Remix OS for PC is a productivity focused, desktop version of Android.
Researching Wii U emulation
Original Xbox Emulator for Windows, macOS, and Linux
Fast PlayStation 1 emulator for x86-64/AArch32/AArch64
DS emulator, sorta
Try Customization Android-x86 OS is Faster, lighter than Emulator with
Emulator for rapid prototyping of Software Defined Networks
Run DOS applications in Windows.
xBRZ: "Scale by rules" - high quality image upscaling filter by Zenju
HLE 3DS emulator
Mesen is a cross-platform (Windows & Linux) NES/Famicom emulator
DOSBox Staging is a modern continuation of DOSBox
Experimental PlayStation Vita emulator
Qt-based Nintendo Entertaiment System emulator and NSF/NSF2/NSFe Music
An experimental Symbian OS emulator
Third-party TI-84 Plus CE / TI-83 Premium CE emulator
A work-in-progress PlayStation 4 emulator
Emulator of NES, SNES, Sega Mega Drive, GameBoy video consoles
Appliances of free/open source operating systems for VirtualBox
Complete BIOS & firmware collection for retrogaming emulators