Lemoniscate - A modern Hotline Server for 10.4/10.5 Macs

A native C and Objective-C implementation of the Hotline protocol for Mac OS X 10.4 Tiger and 10.5 Leopard on PowerPC. This project is a ground-up port of Mobius, a modern Hotline server and client written in Go by Jeff Halter.

What is this?

This is a from-scratch (well, Agentic) rewrite of the Mobius Hotline server and client in C and Objective-C, targeting the PowerPC Macs that Hotline was originally built for. The goal is a native, lightweight binary that runs on PPC Macs (10.4 and 10.5).

See the releases for the latest version!

Why not just fork Mobius?

Mobius is written in Go. Go ironically does have PowerPC support but it never supported Mac OS X 10.4 or 10.5, and it dropped PowerPC support a long time ago. There is no way to compile Go code for Tiger or Leopard on PPC.

Instead, this project uses Mobius as a reference implementation. The C code is structured to mirror the Go source files one-to-one, so when Mobius adds features or fixes bugs upstream, those changes can be traced directly to the corresponding C files here. It is a spiritual port, not a fork.

What is Hotline?

Hotline was a client-server platform from the late 1990s that combined file sharing, group chat, instant messaging, and a news bulletin board into a single application. It was especially popular on the Mac and had a devoted community through the early 2000s. Hotline servers were run by individuals and small communities, each with their own files, chat rooms, and culture. Think of it as a self-hosted Discord from 1997, minus the voice chat and plus a built-in file server.

The Hotline protocol is a binary, big-endian, TCP-based protocol. This is actually a nice fit for PowerPC, which is also big-endian -- the wire format maps directly to native memory layout with no byte-swapping required.

Project structure

The codebase is split into two layers that mirror the Go package structure:

• include/hotline/ and src/hotline/ -- Core protocol library: wire format parsing, serialization, handshake, user/access types, text encoding, and the Objective-C client. Builds into libhotline.a.
• include/mobius/ and src/mobius/ -- Server application: transaction handlers, YAML-based persistence (accounts, bans, threaded news), configuration loading, and runtime server behavior.
• src/gui/ -- Native AppKit admin GUI (lemoniscate-gui) that launches and supervises lemoniscate.
• docs/ -- Operator and implementation documentation.

Quickstart to rolling your own (CLI server)

1) Build

On modern macOS:

make all

2) Initialize config directory

./lemoniscate --init -c ./config

This creates:

• config/config.yaml
• config/Users/*.yaml (including admin and guest)
• config/Agreement.txt
• config/MessageBoard.txt
• config/Banlist.yaml
• config/Files/

3) Start server

./lemoniscate -p 5500 -c ./config

Clients connect on port 5500 (file transfers use 5501).

Quickstart (GUI)

1) Build GUI and app bundle

make gui
make app

2) Launch app bundle

open Lemoniscate.app

The app launches Lemoniscate.app/Contents/MacOS/lemoniscate-server through NSTask.

Important caveats:

• make app checks that lemoniscate and lemoniscate-gui have matching CPU architectures.
• Use APP_SKIP_ARCH_CHECK=1 make app only when intentionally bypassing that safety check.
• The GUI creates the config directory if missing, but does not scaffold full default files; run --init first for a complete setup.

Feature status

Chat & Messaging

• Public chat room with all connected users
• Private chat rooms — create, invite users, set topics
• Instant messages (private messages between users)
• Auto-reply when a user is away or idle
• /me action messages
• Admin broadcast messages to all users

User Management

• User accounts with login and password (salted SHA-1 hashed)
• Guest access (no login required)
• 41 individual permission bits per account
• Admin account editor — create, modify, rename, and delete accounts
• Batch account editing (v1.5+ multi-user editor)
• Kick/disconnect users (with optional message)
• Protected accounts that can't be disconnected

File Sharing

• Browse server files and folders
• Download files with progress tracking
• Upload files to the server
• Download entire folders (recursive)
• Upload entire folders (recursive)
• Resume interrupted downloads
• File info — type, creator, size, dates, comments
• Rename, move, and delete files and folders
• Create new folders
• Create file aliases (symlinks)
• 70+ file type mappings for correct Mac type/creator codes

News & Message Board

• Flat message board (classic Hotline "News")
• Threaded news with categories and articles
• Create and delete news categories
• Post, read, and delete articles with threading
• News data persists across server restarts

Server Administration

• GUI admin application (Cocoa, native Tiger look)
• Setup wizard for first-time configuration
• macOS plist configuration (native format)
• YAML fallback for compatibility
• Server agreement displayed on login
• Server banner image
• Default banner bundled with the app
• Start, stop, and restart from the GUI
• Live server logs in the admin interface
• Log file saved to Application Support

Networking

• Hotline protocol on port 5500 (configurable)
• File transfers on port 5501
• Bonjour/mDNS for local network discovery
• Tracker registration (UDP, periodic with live user count)
• Idle/away detection (5 minutes, auto-broadcasts status)
• Per-IP rate limiting
• Ban list (IP addresses and usernames)

Access Control

Granular per-account permissions including:

• Download, upload, delete, rename, and move files
• Create folders and file aliases
• Read and send chat
• Create and manage private chat rooms
• Read, post, and delete news articles
• Create and delete news categories
• View and modify user accounts
• Disconnect other users
• Send broadcast messages
• Upload location restrictions (Uploads/Drop Box only)
• Drop box folder visibility control

Compatibility

• Runs on Mac OS X 10.4 Tiger (PowerPC)
• Works with Hotline Navigator, the mierau Swift client, and classic Hotline clients
• FILP file transfer format with INFO and DATA forks
• Hotline 1.8+ protocol (version 190)
• CLI server binary for headless operation
• Mobius-compatible account and news file formats

Building

On modern macOS for development and testing:

make all       # build libhotline.a + lemoniscate
make test      # build and run tests
make gui       # build GUI binary
make app       # build Lemoniscate.app bundle

On Tiger with Xcode 2.x, uncomment Tiger flags in Makefile:

CC = gcc-4.0
CFLAGS += -mmacosx-version-min=10.4 -I/usr/local/include
OBJCFLAGS += -mmacosx-version-min=10.4 -I/usr/local/include
YAML_LDFLAGS = -L/usr/local/lib -lyaml

Dependencies:

• CoreFoundation (ships with Tiger)
• Foundation (ships with Tiger)
• AppKit (for GUI)
• pthreads (ships with Tiger)
• libyaml (via Tigerbrew or source build)

Documentation

• Server reference
• GUI reference
• Docs index

Related projects

• Mobius -- The Go implementation this project is based on
• mobius-macOS-GUI -- A SwiftUI wrapper around Mobius for modern macOS

Why "Lemoniscate"?

A lemniscate is the mathematical name for the infinity symbol -- the figure-eight curve that is closely related to the Mobius strip in topology. Both are continuous, single-surface loops. This is a stupid pun and it's an original name.

License

This project is a clean-room implementation referencing the Mobius source code. See the Mobius repository for its licensing terms.