Download Cuis from the GitHub repository:
Issue tracker + latest updates.

Release notes
for all Cuis versions.

You can run Cuis with Squeak's official Virtual Machines from or the faster Cog VMs from Eliot Miranda's site. (Please use the non-MT variants of Eliot's latest release.)

Please read:
Code Management in Cuis
Using GitHub for Cuis packages

Cuis is free software, done mostly by volunteer effort. Finantial support is scarce. You can help up keep developing it with your donation.



Cuis Smalltalk


"Yay, Juan. You GO, guy! ...a great example of malleable software (and a clever mind) at work."
Dan Ingalls

"I like it... It's nice and clean and simple and pretty. Nice stuff!"
Alan Kay

"I think you have a very elegant design aesthetic."
John Maloney

Cuis is:


    - Simple

    - Small

    - Clean


Like Squeak, Pharo and other Squeak variants, Cuis is also:


    - Open Source

    - Multiplatform


Like other Smalltalk-80 environments (including Squeak, Pharo and others), Cuis is also:


    - A complete development environment written in itself

    - A pure Object Oriented language


Cuis is a free Smalltalk-80 environment originally derived from Squeak ( with a specific set of goals: being simple and powerful. It is also portable to any platform, fast and efficient. This means it is a great tool for running on any hardware, ranging from phones and tablets up to personal computers and servers.

Cuis is different from other Squeak variants in that it takes an active attitude towards system complexity: As systems grow older, they usually become more complex. New features are added as layers on top of whatever is below, sometimes without really understanding it, and almost always without modifying it. Complexity grows without control. At some point, the system can't evolve anymore and becomes "legacy code". The only way to avoid this is by understanding the complete system, and reengineering the whole system all the time. Keeping it simple and consistent.

This is important. Complexity puts a limit to the level of understanding of the system a person might reach, and therefore limits the things that can be done with it. Dan Ingalls says all this in "Design Principles Behind Smalltalk". Even if you have already done so, please go and read it again!

With respect to code quality, Casey Ranseberger said "Because we are volunteers without deadlines, we can raise the bar as far as we like; in Cuis, we want to set that bar as high as we can reach. We want to have to jump in order to touch it. But, perhaps paradoxically, we also want to ship often, and we can respond to defects with the same speed we experience in any (good) software engineering organization. In short: Cuis gives us the best of both worlds."

You can see the Cuis and Morphic 3 talk at the Smalltalks conference in Buenos Aires here.

Cuis is continuously evolving towards simplicity. Each release is better (i.e. simpler) than the previous one. At the same time, features are enhanced, and any bugs fixed. Cuis includes recent enhancements from Squeak, but only those that meet Cuis objectives: stuff whose complexity outweighs its utility is skipped.


Nice comments about Cuis:

In addition to those quotes from my big heros at the top, these are from other prominent members of the Smalltalk community:

"Cuis represents the best of Squeak: Elegant simplicity, high quality, and a sense of vision... I really do appreciate Cuis."
"It has a clean, crisp feel and is a pleasure to use."

David T. Lewis

"It's one of the smallest, definitely the fastest, and probably the best structured (Squeak) kernel that has been built."
Andreas Raab

"If you would like to see Morphic done beautifully, ...check out Cuis. ...I simply cannot rave enough about how wonderful an experience it's been to work with."
Casey Ransberger

Some of the main ideas and objectives for Cuis are:

  • Close to the ideas in Smalltalk-80 and "Design Principles Behind Smalltalk".

  • Includes only kernel functionality + dev tools.

  • Included code should be of high quality.

  • Includes a greatly simplified and enhaned Morphic as the main UI.

  • Easy to fix and extend.

  • Reasonably stable. Smalltalk kernel should not change much.


What is the audience? Cuis should be the Smalltalk of choice to:

  • Smalltalkers who want a simple and consistent system they can really master.

  • Teachers and students learning Smalltalk.

  • Developers working for devices with little memory or CPU power.

  • People wanting to experiment with new directions in language design, UI frameworks, etc.

  • People wanting a reasonable kernel on which to build optional packages.



Back compatibility goes against progress. We choose progress. Back compatibility requires extra complexity, of the non-essential kind. We choose simplicity. This means that there are no guarantees of compatibility between Cuis and anything else, including the various releases and derivatives of Squeak, or even other releases of Cuis itself.

However, Cuis is maturing, and changes start to be less drastic. The level of compatibility between Cuis version is increasing.

Besides, Cuis is compatible to a large degree with Squeak. The only area where this might be an issue is Morphic, as it is what has changed most.


Cuis has a young community of developers and users. We have a mail list. You are welcome here!

We want to share fixes, enhancements, packages, and discussion with Squeak and other Squeak distributions. Many of us are also part of the Squeak and Pharo communities.


Past Sponsors

Thanks, Folks!



Cuis is free software, done mostly by volunteer effort. Finantial support is scarce. You can help up keep developing it with your donation.



Cuis is distributed subject to the MIT License, as in . Any contribution submitted for incorporation into or for distribution with Cuis shall be presumed subject to the same license.

Portions of Cuis are:
Copyright (c) Xerox Corp. 1981, 1982
Copyright (c) Apple Computer, Inc. 1985-1996
Copyright (c) Contributors to Squeak and Cuis projects. 1997-2013

   2006-2013 Juan M. Vuletich