s7 is a Scheme implementation intended as an extension language for other applications. It is descended from tinyScheme, and tries to be compatible with the r5rs and r7rs Scheme standards.
s7's real home page is ccrma.stanford.edu/software/snd/snd/s7.html. (See also Carlos Carrasco's "A love letter to s7 Scheme".) The s7 maintainers periodically release new tarballs, with the only version number being in the main header file. The releases archived here in the Conservatory come from 2016-11-18 and 2016-11-21.
s7 is open source software, under a somewhat informally applied BSD-style open source license. The source code quotes the Snd license, since s7 is the default extension language for Snd, and s7's maintainers appear to also be the Snd maintainers. The exact license wording in s7 is:
apparently tinyScheme is under the BSD license, so I guess s7 is too. Here is Snd's verbiage which can apply here: The authors hereby grant permission to use, copy, modify, distribute, and license this software and its documentation for any purpose. No written agreement, license, or royalty fee is required. Modifications to this software may be copyrighted by their authors and need not follow the licensing terms described here. followed by the usual all-caps shouting about liability.
Copyright (c) 2000, Dimitrios Souflis All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. Neither the name of Dimitrios Souflis nor the names of the contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
...which, as you can see, is not quite the same wording as the Snd license.
Either way, however, s7 is essentially under a BSD-style open source license.