| RCA Studio II | An in-browser RCA Studio II (1977): the authentic system ROM on a hand-written RCA 1802 core with CDP1861-style video and twin keypads, plus a full debugger. Boots a cartridge to graphics. | online |
| RISC-V (Linux) | In-browser RISC-V machine (TinyEMU compiled to WebAssembly) that boots a Buildroot Linux to a busybox shell, with a full RISC-V CPU debugger. | online |
| RPCEmu | Open-source emulator of Acorn's Risc PC and A7000 that boots RISC OS. | downloadable |
| Rainbow | Closed-source Windows emulator for the Atari 400/800/XL/XE and 5200 by Chris Lam. | downloadable |
| RealSpectrum | DOS and Windows ZX Spectrum emulator noted for early cycle-accurate emulation. | downloadable |
| Red Squirrel | Freeware Windows emulator of ARM-based Acorn machines by Graeme Barnes. | downloadable |
| Regen | Accuracy-focused freeware Sega 8/16-bit emulator by AamirM. | downloadable |
| Retro Virtual Machine | Freeware ZX Spectrum and Amstrad CPC emulator with authentic CRT visuals and a virtual tape deck. | downloadable |
| RetroArch | A single front end that loads dozens of emulator "cores" through libretro. | both |
| Robotron KC85/3 | The East-German KC85/3 home computer (U880 / Z80), emulated in WebAssembly from floooh's chips project, boots to the CAOS 3.1 menu. | online |
| Robotron Z1013 | The East-German Robotron Z1013 single-board home computer (U880 / Z80, 1985), emulated in WebAssembly from floooh's chips project, boots to its resident monitor prompt. | online |
| Roland | JavaScript Amstrad CPC emulator with sound by Antonio Villena. | online |
| Rosalie's Mupen GUI | Modern Qt front-end and distribution of the Mupen64Plus Nintendo 64 emulator. | downloadable |
| RuMSX | Multilingual Windows emulator of the MSX, MSX2, MSX2+ and turbo R. | downloadable |
| redream | Fast, user-friendly Sega Dreamcast emulator with high-resolution rendering. | downloadable |
| reicast | Multiplatform open-source Sega Dreamcast emulator, the basis for Flycast. | downloadable |