servermacXserver: a rootless X11 server for macOS, built in 30 days
macXserver is a rootless X11 server for macOS. It displays classic X11 clients, the kind that run on vintage Unix workstations, as native, full-resolution Mac windows. It’s a reasonably complete reimplementation of the X11R6 server spec and the SHAPE extension, written from scratch in Swift on modern macOS Core Graphics. It ships with its own window manager and resource editor, so there is nothing else to install.
I wrote the bulk of it over 30 days using Claude Code, the agentic software development tool. The goal was a server to support my collection of Sun computers, documented at oldsilicon.com . It’s free. Grab the signed, notarized binary from the Download page, or build it yourself from the source on GitHub .
Here is the 30-Day Sprint build log.
Features
What macXserver does differently. Each card opens a page with more screenshots and the technical detail.
Display scaling without changing your desktop
Pick the size of X windows independent of the rest of the desktop. macXserver windows scale on their own.
Scalable Mac fonts through core X11
Every X font request maps to a Core Text font at integer pointSize. No bitmap catalog on disk, no client-side Xft setup, no compile flags. Just the standard core X11 font path with scalable Mac fonts on the other end. Anti-aliased throughout.
X windows are first-class macOS windows
One NSWindow per X top-level. Real Mission Control behavior. Optional Motif-style window frame when you want it.
Session capture and replay
Capture-first was the methodology for the whole project. The framer and proxy were Day 1, before a single opcode handler. Every byte of every session can be recorded to a .xtap file and replayed against another server.
Remote app launcher
One click from the Mac status menu to an X client running on a vintage Sun, or a modern Linux/BSD box over SSH. Passwords in Keychain, optional verbose progress, two-stage menu grouped by host.
Shaped windows: oclock, xeyes, and friends
Round windows and oval windows that stay round at Retina device scale. The SHAPE mask gets traced to a CGPath and rasterized at the window's actual backing resolution, so the edges of oclock and xeyes don't stairstep. The Motif frame plays along.
Built-in resource editor with themes
Edit the X RESOURCE_MANAGER from inside macXserver. Theme switching, line-numbered code editor, reload without restart.
Map X font names to Mac fonts
X clients ask for fonts by classic names like 'fixed' or 'helvetica'. macXserver maps each one to a real Mac font. The mapping is user-editable and lives in a single small file.
The 30-Day Sprint
One short entry per day. What landed, what clicked, what got chased and didn't pan out.