MoofTCP: a from-scratch MacTCP replacement for 68k Macs running System 6

A drop-in replacement for Apple's 1990s stack

MoofTCP is an open-source project, published on GitHub by matthewmrichter, that replaces Apple's MacTCP networking software on Motorola 68000 Macintoshes running System 6. It drew wider attention after appearing on the Hacker News front page.

According to the project's page, applications written for MacTCP run unchanged because MoofTCP implements the same .IPP driver interface — covering TCP, UDP and ICMP echo — together with the dnrp name resolver. Behind that familiar interface sits a TCP/IP stack written from scratch in portable C, plus its own control panel, installer and DHCP client. The stated target machine is a Mac Classic with 4 MB of RAM, and the project says that tight memory budget shaped the engineering throughout.

The motivation is that MacTCP, while functional, shows its age: on a 4 MB Classic paired with a SCSI Wi-Fi/Ethernet adapter such as BlueSCSI, it can be sluggish to respond, heavy on memory and awkward to configure. MoofTCP therefore aims, in order, for reliability (avoiding hangs and leaks when programs exit), low latency for interactive use such as telnet sessions, and throughput — all while using no more resident memory than MacTCP.

What ships in the box

Beyond the stack itself, the project provides:

• A choice of DHCP or a fixed address, picked in the control panel.
• MoofTCP Lite, a build without DHCP that saves roughly 5 KB of system memory for tight machines; a single installer holds both versions, selected with a checkbox.
• An installer that moves MacTCP's files aside, restores them exactly on removal, and repairs itself if an install is interrupted.
• MultiFinder awareness, so connections left open by a quitting application are cleaned up.
• Diagnostics: an optional in-memory log and a small MoofDiag tool for producing bug reports.

Tested hardware and software

The project reports testing on a real Mac Classic running System 6.0.8 with 4 MB of RAM and a BlueSCSI v2 WiFi adapter with DaynaPORT, as well as in the Snow emulator. The telnet terminal Flynn and Wikipedia Reader work on both; MacTCP Watcher, NCSA Telnet, Fetch and TurboGopher work in the emulator; Eudora launches, though mail handling was not tried. Requirements are a 68k Mac on System 6.0.8 and an Ethernet adapter that supplies the .ENET0 driver — MoofTCP ships no Ethernet driver of its own, and the project asks users to report results on other system versions.

On memory, the full driver occupies 95,623 bytes of code and the Lite build 90,722 bytes; after the driver's first open on a real Mac Classic under single Finder, about 30.7 KB of system heap remained free.

How it is built

The portable core avoids malloc and global state, and is tested on modern desktops with AddressSanitizer and UBSan enabled by default, alongside fuzzers, through CMake and ctest. Cross-compiling for the Mac needs only Docker, which pulls a pinned Retro68 toolchain image automatically. The code is MIT-licensed and, per the README, contains no Apple or third-party code. One credit stands out for a project aimed at decades-old hardware: the README says Claude Code was used to develop it, with human planning and testing.

Known limitations include no IPv6, testing only against the DaynaPORT driver on System 6.0.8, and a deliberately basic DHCP client — no lease RELEASE, no INIT-REBOOT, no address-conflict probe, and UDP port 68 is unavailable to other programs while DHCP runs. If no DHCP server is present, the first open waits about ten seconds before failing. The roadmap hints at MoofPort, a similar rework of the DaynaPORT driver, along with closer integration with BlueSCSI.

Why it matters

Adapters like BlueSCSI have made it straightforward to give decades-old Macintoshes storage and network links, but the system software underneath has not kept pace: MacTCP is proprietary, dated and fiddly to configure. MoofTCP closes that gap with a from-scratch stack that existing vintage applications can use unchanged, that is verifiable with modern sanitizers and fuzzers, and that carries a permissive license. It is also a tidy example of contemporary development practice — containerized cross-compilation and AI-assisted coding — reaching all the way back to a 68000-era platform. For anyone keeping a System 6 machine in service, networking that installs with a checkbox and reverts cleanly is a genuine quality-of-life improvement.