Emscripten is available under 2 licenses, the MIT license and the
University of Illinois/NCSA Open Source License.

Both are permissive open source licenses, with little if any
practical difference between them.

The reason for offering both is that (1) the MIT license is
well-known, while (2) the University of Illinois/NCSA Open Source
License allows Emscripten's code to be integrated upstream into
LLVM, which uses that license, should the opportunity arise.

The full text of both licenses follows.

==============================================================================

Copyright (c) 2010-2014 Emscripten authors, see AUTHORS file.

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.

==============================================================================

Copyright (c) 2010-2014 Emscripten authors, see AUTHORS file.
All rights reserved.

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the
"Software"), to deal with 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:

    Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimers.

    Redistributions in binary form must reproduce the above
    copyright notice, this list of conditions and the following disclaimers
    in the documentation and/or other materials provided with the
    distribution.

    Neither the names of Mozilla,
    nor the names of its contributors may be used to endorse
    or promote products derived from this Software without specific prior
    written permission. 

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 CONTRIBUTORS 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 WITH THE SOFTWARE.

==============================================================================

This program uses portions of Node.js source code located in src/library_path.js,
in accordance with the terms of the MIT license. Node's license follows:

    """
        Copyright Joyent, Inc. and other Node contributors. All rights reserved.
        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.
    """

The musl libc project is bundled in this repo, and it has the MIT license, see
system/lib/libc/musl/COPYRIGHT

The third_party/ subdirectory contains code with other licenses. None of it is
used by default, but certain options use it (e.g., the optional closure compiler
flag will run closure compiler from third_party/).