JSON for Modern C++ contains code under licences of its own, as its README states.

The UTF-8 decoder from Bjoern Hoehrmann, licensed under the MIT License.
Copyright (c) 2008-2009 Björn Hoehrmann <bjoern@hoehrmann.de>

A slightly modified version of the Grisu2 algorithm from Florian Loitsch, licensed under the MIT License.
Copyright (c) 2009 Florian Loitsch

A copy of Hedley from Evan Nemerson, licensed as CC0-1.0.

Parts of Google Abseil, licensed under the Apache License 2.0, whose text is listed under Roboto.

The MIT License:

MIT License

Copyright (c) <year> <copyright holders>

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.
