Cuis is:

  • Small and Clean,
  • Free Software,
  • Multi-platform.

Like any Smalltalk systems, it is also:

  • A complete development environment written in itself,
  • A pure, dynamic Object Oriented language.

Cuis assumes very little on the underlying platform, and this lets it run out-of-the-box on Windows, MacOS, Linux, ChromeOS and WebBrowsers. Cuis shares the OpenSmalltalk Virtual Machine with Squeak, Pharo and Newspeak.


Code management in Cuis is done with its package system and your preferred VCS. Cuis development is done on GitHub.
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Refactoring tools

The Cuis source code browser is equipped in standard with a set of refactoring features.
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What sets Cuis apart from the other members of the Squeak family is the focus on the original values of the Smalltalk project at Xerox PARC, and an active attitude towards system complexity:

Unbound complexity growth, together with development strategies focused only in the short term, are the worst long term enemies of all software systems. 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 and size grow without control. Evolution slows down. Understanding the system becomes harder every day. Bugs are harder to fix. Codebases become huge for no clear reason. At some point, the system can’t evolve anymore and becomes “legacy code”.

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!

Morphic 3

This framework's aim is to build the next standard in 2D user interface. It is zoomable and rendered with its high quality Vector Graphics back-end. It's entirely written with Cuis and accelerated with a plug-in.
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Small & Simple

Smalltalk is a very compact and coherent programming language. Cuis is a very compact Smalltalk implementation. The user ability to understand the system is one of the major concern of the Cuis' community.

Cuis Smalltalk is our attempt at this challenge. Furthermore, we believe we are doing something else that no other Smalltalk, commercial or open source, does. We attempt to a the true Smalltalk-80 experience, and keep Smalltalk-80 not just as legacy software of historic significance, but as a live, evolving system. We feel we are the keepers of this Smalltalk heritage, and enablers of the Dynabook experience.

As Cuis evolves, we keep on these values. Every update, be it a bug fix or a feature enhancement, is reviewed carefully to avoid adding unneded complexity to the system. Every opportunity to remove unneded complexity is followed. As we go, features are enhanced, and any reported bugs fixed. We also adopt selected enhancements from Squeak and Pharo, and share our work with the wider Smalltalk community.


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 project. 1997-2022

Copyright (c) Contributors to Cuis Smalltalk project. 2009-2022