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A Sinclair QL in your browser — a 68008 at 7.5 MHz, the ZX8301 and ZX8302, the IPC's keyboard and BEEP sound, and two microdrives — booting the open-source Minerva ROM into SuperBASIC. Type in or paste listings, read and write .mdv cartridge images, and assemble 68000 code with a debugger.
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Write 8086 assembly in NASM syntax and step through it as a DOS .COM program: every instruction's bytes split into prefix, opcode, ModR/M, displacement and immediate with each field explained, registers and flags with changes highlighted, segment:offset addresses with the 20-bit physical address, Intel's clock count for every instruction (8086 or 8088), an 80 × 25 colour text screen at B800:0000, BIOS and DOS interrupts, and the keyboard.
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Write Cortex-M assembly and step through it on a simulated microcontroller: a GNU-syntax assembler for Thumb and Thumb-2 with literal pools and IT blocks, every 16- and 32-bit encoding split into its fields bit by bit, registers and NZCV with changes highlighted, memory and stack views, breakpoints, LEDs and switches on GPIO, a UART terminal, SysTick interrupts through a vector table, and Cortex-M0 or M3 cycle counts.
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An Acorn Electron in your browser — the Electron ULA with MODEs 0–6, its palette registers and the RAM contention that slows the CPU in MODEs 0–3, the single sound channel, the keyboard matrix and UEF tapes through the ULA's cassette interface — with your own Acorn ROMs or an open stand-in OS. Type BBC BASIC, write 6502 assembly and debug it with breakpoints beside the code.
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Write, assemble, run and debug CHIP-8, SUPER-CHIP 1.1 and XO-CHIP programs in an Octo-style assembly language — an interpreter with the well-known quirks as switches, 60 Hz timers, sound and XO-CHIP's audio patterns, a keypad, breakpoints, registers, memory and a disassembler, with eight example programs. Load your own .ch8 files.
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A Commodore PET in your browser — the 2001, 3032 and 4032 with the 40-column screen, or the 80-column CBM 8032; graphics or business keyboard, green, white or amber phosphor, the CB2 beeper, the 6520 PIAs and the 6522 VIA. It boots Microsoft's open-source BASIC 1.1 on a KERNAL written for this site, or your own ROMs; loads PRG, D64 disks and TAP tapes, and saves to them. Write 6502 assembly and debug it beside the code.
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A Commodore VIC-20 in your browser — PAL or NTSC, unexpanded or with 3 to 35 KB of expansion, the VIC chip's 22 × 23 screen, colours, multicolour and custom characters, its three voices and noise, both 6522 VIAs, keyboard and joystick (gamepad too). It boots Microsoft's open-source BASIC 1.1 on a KERNAL written for this site, or your own ROMs; loads PRG, D64 disks, TAP tapes and cartridges, and saves to disk and tape. Write 6502 assembly and debug it beside the code.
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A Dragon 32, Dragon 64 or TRS-80 Color Computer 2 in your browser — a cycle-counted Motorola 6809, the SAM 6883, the MC6847 VDG with every text, semigraphics and graphics mode (and NTSC artifact colours), both 6821 PIAs, the 6-bit DAC, joysticks, CAS tapes, cartridges — with your own BASIC ROMs or an open 6809 monitor. Write 6809 assembly and debug it with breakpoints beside the code.
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The Jupiter Ace — the 1982 home computer that booted into Forth — in your browser on its own ROM: type Forth through its line editor, watch the dictionary grow, call Z80 code from Forth with a debugger, and load and save .TAP tapes and .ACE snapshots.
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A real Linux booted in the page (a small kernel and BusyBox in the v86 x86 emulator) with a terminal, sample logs, CSVs and a config tree in your home directory, and 26 exercises — text pipelines, find and xargs, redirection, permissions, processes and signals, environment variables, loops — that check your answer.
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A Memotech MTX500, MTX512 or RS128 in your browser — Z80 at 4 MHz, the TMS9929A video chip, the SN76489 sound chip, the Z80 CTC's interrupts, the IOBYTE memory paging, the keyboard matrix and .MTX tapes — running your own Memotech ROMs for MTX BASIC, or an open stand-in monitor, with a Z80 assembler, examples and a debugger with breakpoints beside the code.
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An Oric Atmos or Oric-1 (16K or 48K) in your browser — the ULA's 40×28 text and 240×200 HIRES with serial attributes, the 6522 VIA, the AY-3-8912, the keyboard matrix, and .TAP tapes loaded and saved at once through ROM traps. Write 6502 assembly and debug it with breakpoints, stepping, registers, memory and chip views. Load your own BASIC ROM; without it a stub monitor written for this site runs.
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Write RV32IM assembly and step through it: an assembler with pseudo-instructions and %hi/%lo, the machine code beside each line with every format's fields decoded bit by bit, registers with changes highlighted, memory and stack views, breakpoints, RARS-style ecalls, LEDs and switches on a memory-mapped device, and a 5-stage pipeline diagram of what ran, with stalls, forwarding and flushes.
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A SAM Coupé in your browser — the 6 MHz Z80 with memory contention, all four screen modes, the 128-colour palette, line interrupts, LMPR/HMPR/VMPR paging, SAA1099 stereo sound, the keyboard and mouse, and MGT/SAD/DSK disks through a VL1772 — booting SAM ROM 3.0 to SAM BASIC, with a Z80 assembler, examples (mode 4 palette cycling, raster bars, SAA1099 music) and a debugger.
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A TRS-80 Model I or Model III in your browser — the 64 × 16 screen with its 2 × 3 block graphics, the memory-mapped keyboard, the clock interrupt, cassette sound, .CAS tapes and .CMD programs — booting GW-80, an open monitor ROM written for this page (or your own Level II ROM for BASIC), with a Z80 assembler, examples and a debugger.
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Test a game controller in the browser — every button and axis live, stick drift and a suggested dead zone, a circularity score, trigger range, button chatter, polling rate and rumble — and build an SDL GameControllerDB mapping for pads the browser doesn't know.
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An Amstrad CPC 464 and 6128 in your browser with the original firmware and Locomotive BASIC, a Z80 assembler and debugger with the firmware's jumpblock names, live views of the Gate Array, CRTC, PPI, AY and floppy controller, and DSK, CDT and SNA support.
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An Apple II+ or IIe in your browser — text, lo-res and hi-res with NTSC artifact colour or a monochrome monitor, the speaker, and a Disk II that reads .DSK, .DO, .PO, .2MG and .NIB images as real GCR nibbles. Write 6502 assembly and debug it with breakpoints beside the code, stepping, registers, memory and the soft switches. Load your own ROMs; without them a stub monitor written for this site runs.
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A BBC Micro Model B in your browser — 6845 CRTC and video ULA (MODEs 0–7 with MODE 7 teletext), both 6522 VIAs, the SN76489, UEF tapes and SSD/DSD discs through an emulated 8271 — with your own Acorn ROMs or an open stand-in OS. Type BBC BASIC (inline [ ] assembler included), write 6502 assembly, and debug with breakpoints beside the code, stepping, OS call labels and chip views.
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A Commodore VIC-20 (PAL or NTSC, with memory expansions and cartridges) or PET 2001 / 3032 / 4032 / 8032 on one page — the VIC chip's video and sound, the 6522 VIAs and 6520 PIAs, the keyboards, PRG, D64 and TAP files. Boots Microsoft's open-source BASIC 1.1 on a KERNAL written for this site, or your own ROMs. Write 6502 assembly and debug it with breakpoints beside the code.
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An MSX1 in your browser — TMS9918A video (every mode, sprites, fifth-sprite and collision flags), AY-3-8910 sound, slots, mapper cartridges with Konami SCC, and .CAS tapes — booting the open-source C-BIOS (or your own MSX BIOS for BASIC), with a Z80 assembler, MSX examples and a debugger with breakpoints beside the code, VDP, PSG and slot views.
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One toolkit for retro disk and tape images — Amiga ADF, C64 D64/D71/D81/T64/TAP, Atari ATR and ST/MSA, Amstrad CPC and Spectrum +3 DSK, ZX TAP/TZX, BBC SSD/DSD, Apple II DOS 3.3 and ProDOS, MSX and PC FAT — auto-detected; browse, view files as hex, text in the machine's own character set, listed BASIC or pictures; add, delete and rename; create blank disks, convert, and open them in the emulators.
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An Amiga in your browser — vAmiga compiled to WebAssembly, booting the free AROS Kickstart or your own ROM. Boot your own ADF disks on an A500 or an A1200.
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Write Atari 2600 (VCS) programs in 6502 assembly — DASM-style, with vcs.h and macro.h built in — assemble them to a 2K, 4K or 8K cartridge, and run them in an emulator with a debugger: step by instruction, scanline or frame, breakpoints, registers, RAM, TIA state, the beam position, and a frame-timing check.
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A ZX Spectrum 48K and 128K and a Timex Sinclair TS2068 / TC2068 in your browser, with the original ROMs, a Z80 assembler and a debugger — assemble and run example programs (including Timex hi-res and hi-colour), set breakpoints, step through code, and inspect registers, memory, bank maps and screen addresses. Loads TAP, TZX, SNA, Z80 and DCK files.
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A Sinclair ZX81 (1K or 16K) in your browser running the original ROM, with a Z80 assembler that builds REM-statement programs, a debugger with breakpoints and single-stepping, and .P file loading and saving.
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An Atari 800, 800XL or 130XE in your browser (atari800 in WebAssembly, the free Altirra OS and BASIC) — run disks, programs, cartridges and tapes; type and save BASIC; write 6502 assembly and run it, or call it from BASIC with USR; and debug anything that runs with breakpoints, stepping, registers, memory, the ANTIC/GTIA/POKEY/PIA registers and the display list.
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An Atari ST or STE in your browser — Hatari compiled to WebAssembly, booting the free EmuTOS. Put disk images in A: and B:, programs on an emulated hard disk C:, autostart a program, play with keys or a gamepad, save states, and convert MSA ⇄ ST images.
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A Commodore 64 in your browser — the cycle-stepped chips emulator in WebAssembly, booting the free MEGA65 Open ROMs (or your own). Run PRG, D64, T64 and TAP files; type and save BASIC; write 6502 assembly and run it, or call it from BASIC with SYS; and debug anything that runs with breakpoints beside the code, stepping, registers, memory, and the VIC-II, SID and CIA registers.
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Explore Amiga .adf and .adz floppy images in the browser — bootblock, root block, block map, directory tree with dates, protection bits and comments — extract files or the whole disk as a ZIP, verify checksums, and create new OFS or FFS disks with your own files.
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Write 68000 assembly, build it with the real vasm assembler and vlink linker compiled to WebAssembly, and boot it on an emulated Amiga 500 (vAmiga) with the free AROS Kickstart, or your own ROM. Includes examples, a listing, a hunk view, downloadable ADFs, and the vAmiga debugger.
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Open .ST and .MSA floppy images in the browser — boot sector and BPB, FAT12 cluster map, folders, PRG headers — extract files, convert between ST and MSA, create blank disks, and add files.
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Build FS-UAE and WinUAE / Amiberry configurations for any Amiga from the A1000 to the CD32 — CPU, chipset, memory, Kickstart, floppies, hard drives, RTG and input — with checks for combinations that will not boot, and identify Kickstart ROM files by CRC and header.
Article ·
How I built a modern dev kit for the 3DO Interactive Multiplayer — Norcroft ARM C in Docker, a patched Opera emulator with a GDB server and a JSON control port, and an MCP server — and used it to ship a demo and 21 games.
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A modern development kit for the 1993 3DO Interactive Multiplayer: the original-style Norcroft toolchain in Docker, a patched Opera emulator with a GDB server and remote-control API, and MCP tools for Claude Code.
