| X millennium | Influential Sharp X1 / X1turbo emulator with a Neko Project II-style frontend. | both |
| XM6 Pro-68k | Highly accurate Sharp X68000 emulator for Windows maintained by M.I.J.E.T. | downloadable |
| XM6 TypeG | Sharp X68000 emulator fork by GIMONS focused on game and demo compatibility. | downloadable |
| XM8 | Cross-platform NEC PC-8801mkII SR emulator by PI. derived from the Common Source Code Project. | downloadable |
| XRoar | Cross-platform Dragon and Tandy Color Computer 1/2/3 and MC-10 emulator, also runnable in the browser via WebAssembly. | both |
| XTulator | A portable open-source 8086/80186 PC emulator and the successor to Fake86. | downloadable |
| Xcpc | Portable Amstrad CPC 464/664/6128 emulator for X11-based Unix systems by Olivier Poncet. | downloadable |
| Xebra / Arbex | Highly accurate Japanese freeware PlayStation emulator by Dr. Hell. | downloadable |
| Xemu | Open-source emulator of Commodore 65, MEGA65, Commodore LCD and related 8-bit machines. | downloadable |
| Xerox Alto | Browser-based Xerox Alto emulator (ContrAltoJS): boot the 1973 Xerox PARC workstation that pioneered the GUI, mouse and bitmap display, straight to the Alto Executive. | online |
| Xformer | Long-lived Atari 8-bit emulator by Darek Mihocka, now free as Xformer 10 for Windows. | downloadable |
| Xpeccy | Multiplatform emulator of ZX Spectrum and other retro computers built with Qt and SDL. | downloadable |
| xtrs | Long-running open-source TRS-80 Model I/III/4/4P emulator for Unix and the X Window System. | downloadable |