Squeak is a tightly integrated software development environment for live software construction using the object-oriented programming language Smalltalk. It runs on many computers and operating systems. Squeak is free and open source. Squeak has its own unique place in the universe. A growing community of Squeak developers and users meet here to share facts and pointers to other Squeak related websites.
http://www.squeak.org/ – Squeak's main website, also reachable by clicking on the Squeak mouse icon on the top left
"We believe that, among many other capabilities, Squeak is a valuable research and prototyping platform for various kinds of user interfaces, interaction models, programming paradigms, and educational methods" [source]
As of Squeak v4.0 (which was released back in 2010), Squeak is licensed mostly under the MIT license, with some parts under the Apache 2.0 license. For more details, see FAQ: Licenses
Morphic / Etoys / Scratch
Morphic is a direct-manipulation User Interface (UI) construction kit.
Etoys is a scripting system used in education built on top of Morphic.
Scratch (NuScratch) is a visual programming tool built with Squeak.
Documentation
Documentation – A detailed outline of Documentation on Squeak.
The Squeak Oversight Board coordinates the community’s open-source development of its versatile Smalltalk environment. Read about its mission on its blog.
SqueakSource – Monticello code repository server which hosts your projects. Connect to it with the Monticello Browser from Squeak or use the web frontend.
SqueakMap – The catalogue of available Squeak code, including applications, tools, projects, goodies, packages, etc.
All Projects – Many projects complementing SqueakMap, either because they don't fit there (like hardware), or they are not yet maintained there.
Production Squeak – Squeak code that is being used for commercial or non-commercial applications.
Code requests – Code that's begging to be written, if only someone can find the time.