You do not need to download anything. The Newspeak IDE is a PWA
(Progressive Web App) and can be installed locally on your
machine. If you want a local copy, just navigate to the app
using a web browser that supports PWA installation (any Chromium based
browser,or Safari on iOS).
If you are unwilling to use a browser that supports PWA
installation you can still download an old version of the IDE as
a locally servable Web app, but this is not being updated.
For all platforms.
The Squeak based system and contains code that is subject to the Squeak License, as well as the Newspeak sources, which are mostly under the Apache 2.0 license. More details about the licensing of this software are available on the license page.