Source files below 'platforms/Cross' in this distribution that do not
contain individual copyright and license notices, and

Source files below 'platforms/unix/src' in this distribution that do
not contain individual copyright and license notices are:

  Copyright (C) 1996-2006 by Viewpoints Research Institute and other
                             authors/contributors as listed.

  All rights reserved.

All other source files below platforms/unix in this distribution that do not
contain individual copyright and license notices are:

  Copyright (C) 1996-2006 by Ian Piumarta and other authors/contributors
                             listed in individual source files.

  All rights reserved.

For all of the above files:

  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:

  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.

  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.

--

See http://wiki.squeak.org/squeak/933
See http://wiki.squeak.org/squeak/159

FAQ: Licenses
Last updated at 4:51 am UTC on 18 February 2017
License since Squeak 4.0 is MIT

From the Squeak 4.0 release notes:

Welcome to Squeak - a free, open Smalltalk system.
Squeak 4.0 is the pinnacle of several years of relicensing work. Though this version is functionally equivalent to Squeak 3.10.2, it is the first version of Squeak to be licensed fully under FOSS terms. Squeak 4.0 is licensed under MIT, with some original Apple parts remaining under the Apache 2.0 license.