Hi everyone,

I wanted to share a passion project I've been working on that might be highly useful for the Mac users in this community.

If you work with z/OS on a Mac, you've likely noticed a gap in the tooling: most decent TN3270 clients either come with hefty commercial licensing fees or rely heavily on Java or X11, which can feel out of place on modern macOS. I was frustrated by this, so I spent some time reading through the old IBM GA23-0059 manuals and built a lightweight alternative from scratch.

It's called X3270, and it is completely free and open-source (MIT License). It went surprisingly viral on LinkedIn recently, so I wanted to make sure I shared it with the core community here.

My main goal was to build something that feels like a truly native citizen on macOS while perfectly respecting the classic 3270 data stream.

Here are some of the technical highlights:

• Truly Native: Built entirely in C++ and Objective-C++ on top of native Cocoa and CoreText. No Java and no X11 required.

• Full TN3270E Support: Handles full protocol negotiation including the ISPF Query Reply, so your menus and layouts render correctly right out of the box.

• Modern Security: Supports implicit TLS (TLS 1.2+) on any port via native OpenSSL integration.

• Multiple Screen Models: Dynamically supports Models 2, 3, 4, 5, and a custom Large model (62 × 160) utilizing 14-bit buffer addressing.

• Authentic Look: It ships with the beautiful open-source IBM 3270 terminal font by Ricardo Bánffy bundled directly in the app.

• Export & Capture: Includes features to save pixel-perfect PNG screenshots or export the screen buffer directly to formatted UTF-8 text files.

X3270 runs on macOS 12 Monterey and later, with native support for both Apple Silicon and Intel.

If you are looking for a fast, native, and free way to connect to your mainframes from a Mac, I'd love for you to give it a try.

You can find the pre-built DMGs and the full source code on GitHub here: https://github.com/el-dockerr/X3270

I am always looking for feedback, so feel free to drop your thoughts, bug reports, or feature requests in the thread below or directly on GitHub.

Best regards, Swen

Hello,

A big thank you for sharing and working I use it every day since I switched to Mac OS 4 years ago!

Regards,

François

When you can't open the DMG because it is Damaged, plese check if you choosed the right arch, and follow this instruction:

DX3270 is currently unsigned (a Developer ID certificate is planned for a future release once the remaining bugs are ironed out). macOS will refuse to open it directly. There are two ways around this:

Option A - System Settings (GUI)

1. Try to open DX3270.app - dismiss the "damaged or can't be opened" alert
2. Open System Settings → Privacy & Security
3. Scroll down - a banner appears: "DX3270 was blocked because it is not from an identified developer"
4. Click Open Anyway
5. Confirm in the following dialog - the app launches and macOS remembers the choice

Option B - Terminal (one-time command)

sudo xattr -r -d com.apple.quarantine /Applications/DX3270.app

This strips the quarantine flag that triggers Gatekeeper. After running it, DX3270 opens normally from Finder or the Dock without any further prompts.

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Swen Kalski
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Swen,

I wish I was allowed to connect my Mac at home to our z/OS servers at the office so I could try your tool but I don't think that will be possible.  It sounds like DX3270 has many great features.

Thanks for renaming your project to DX3270 to avoid confusion with the other open-source project called x3270.  We have used several of the x3270 tools for many years at our shop. 

Brad

Maybe the time will bring some thrust on this tool.
I guess new Projects have to ripe and show thrust and stability. But I will be patient and glad when it will be.

I like to see that people like my tool and I'm part of a big and awesome community like IBM and bring something useful to all of you. 

When trying to start the application I'm getting the following dialog box:

You can't use this version of the application "DX3270" with this version of macOS.

I'm on a M3 Mac running Sequoia 15.7.7. I downloaded DX3270-1.7.4-build1.dmg.

Hello Swen,

I am running macOS Sequoia 15.7.7 on an Intel MacBook Pro.  I downloaded the DX3270-1.7.4-build1-Intel.dmg and receive the following error when attempting to run the application:

You can't use this version of the application "DX3270" with this version of macOS.

Just to make sure the macOS Gatekeeper wasn't causing this error as well, I did use xattr to remove it from quarantine, and that made no change in behavior.

Best Regards,

Ted Allen