systemless

Systemless is a high-level runtime for 68k classic Macintosh applications and games, written in Rust.

It interprets guest 68k code with the m68k crate and handles Mac OS A-line traps in native Rust. That lets packaged Mac applications run without a Mac ROM image, a full System install, or hardware emulation.

Marathon	Escape Velocity

Browser demos are available at https://systemless.org/.

Status

Systemless is focused on real 68k applications that use the classic Mac Toolbox. The HLE now covers the major runtime surfaces needed by interactive software:

• Memory Manager handles, pointers, zones, low-memory globals, and common exception paths.
• Resource Manager, Segment Loader, File Manager calls, and an in-memory HFS-like VFS with data and resource forks.
• QuickDraw ports, regions, text, shapes, PICT, CopyBits, color tables, offscreen GWorlds, cursors, and 1bpp/8bpp framebuffers.
• Event, Menu, Window, Control, Dialog, TextEdit, Cursor, Process, Sound, SANE, and common Toolbox utility traps.
• Sound Manager playback, channel state, command queues, callbacks, file playback, and host audio mixing.

It is not a bit-perfect Mac hardware emulator. Hardware-specific services such as slot interrupts, device queues, removable-media behavior, and multi-process system integration are modeled only where guest-visible behavior matters.

Quick Start

cargo install systemless
systemless path/to/app-or-game.sit

The installed systemless command opens a window, renders the guest framebuffer, maps keyboard and mouse input, and enables audio when a host backend is available.

Common runner options:

systemless --headless --max-instructions 5000000 path/to/app.sit
systemless --arrows-as-numpad path/to/game.sit
systemless --show-menu-bar path/to/app.sit
systemless --cpu-mhz 25 path/to/app.sit

Systemless accepts StuffIt archives, MacBinary files, and raw/macOS resource forks. Archives may contain multiple files; Systemless populates the in-memory VFS and selects an executable resource fork from the archive.

Desktop saves are stored next to the launched archive under .systemless/saves/<archive-name>/. For example, launching /Games/EV Override 1.0.1.sit restores and persists saves under /Games/.systemless/saves/EV Override 1.0.1/. The store preserves Mac data and resource forks and is kept separate from the original archive.

Systemless does not ship applications, games, Mac ROMs, or Apple system software. Use legally obtained application archives.

For a local checkout, use cargo run --release -- path/to/app-or-game.sit.

Library Use

Programmatic loading goes through FixtureRunner:

use systemless::runner::{FixtureRunner, FixtureRunnerConfig};

let bytes = std::fs::read("game.sit").expect("read game");
let mut runner = FixtureRunner::new(32 * 1024 * 1024, FixtureRunnerConfig::default());

systemless::game::load_game(&mut runner, &bytes).expect("load game");
let (_steps, _still_running) = runner.run_steps(100_000, None);
runner.composite_frame();

Use systemless::display to render the current framebuffer for custom frontends.

Save Persistence

Systemless keeps the guest filesystem in the runner's in-memory VFS. Persistence is a frontend responsibility: the engine exposes snapshots of VFS files, and a frontend decides where to store them.

Use the FixtureRunner VFS snapshot API for save files:

• vfs_file_summaries() lists VFS files with fork sizes, hashes, and metadata.
• vfs_file_snapshot(path) exports one file's data fork, resource fork, and Finder metadata.
• import_vfs_file(snapshot) restores a previously exported file into the VFS.
• remove_vfs_file(path) removes a file from the VFS.

The expected frontend sequence is:

create runner
load archive into runner
record archive VFS summaries/fingerprints
load stored save snapshots
import_vfs_file(...) for each stored save
init_game(...)
periodically scan vfs_file_summaries()
persist changed user-save snapshots from vfs_file_snapshot(...)
flush one final scan on shutdown

Record the archive fingerprints before importing stored saves. That lets the frontend avoid copying packaged game files into the save store and persist only new or changed user-save files. Save-file filtering is frontend policy; common filters exclude System Folder preferences, temporary items, Trash, and desktop database files.

The built-in desktop runner uses this API and stores snapshots next to the launched archive under .systemless/saves/<archive-name>/.

Crate Map

Build And Test

cargo build --release
cargo test --lib
cargo check --no-default-features
cargo package

The default gui feature enables the desktop runner dependencies: winit, softbuffer, and cpal. Disable default features for headless library builds.

On Linux, the default GUI/audio build also needs ALSA development files for cpal's ALSA backend. Install pkg-config plus your distribution's ALSA dev package before running cargo build --release; for example:

sudo apt install pkg-config libasound2-dev      # Debian/Ubuntu
sudo dnf install pkgconf-pkg-config alsa-lib-devel  # Fedora/RHEL
sudo pacman -S pkgconf alsa-lib                # Arch

Font Data

Systemless does not load TTF files at runtime. The built-in DejaVu-derived glyph bitmaps are generated into src/quickdraw/fonts/baked.rs and compiled into the crate, so an installed systemless binary can render text without external font files.

The TTF files under assets/fonts/ are source assets for regenerating the baked catalogue. If SYSTEMLESS_ORIGINAL_FONTS_DIR is set, Systemless can also load locally generated bitmap override blobs ahead of the baked catalogue.

Useful Environment Variables

References

Trap implementations cite Inside Macintosh, BasiliskII observations, or fixture contracts where that context is useful. The implementation favors guest-visible behavior over cycle or hardware fidelity.

License

GPL-3.0-or-later. See LICENSE.

Bundled DejaVu font assets are covered by their own license in assets/fonts/LICENSE.DejaVu.txt.