JsonCpp
The JsonCpp library’s source code, including accompanying documentation, tests and demonstration applications, are licensed under the following conditions…
The author (Baptiste Lepilleur) explicitly disclaims copyright in all jurisdictions which recognize such a disclaimer. In such jurisdictions, this software is released into the Public Domain.
In jurisdictions which do not recognize Public Domain property (e.g. Germany as of 2010), this software is Copyright (c) 2007-2010 by Baptiste Lepilleur, and is released under the terms of the MIT License (see below).
In jurisdictions which recognize Public Domain property, the user of this software may choose to accept it either as 1) Public Domain, 2) under the conditions of the MIT License (see below), or 3) under the terms of dual Public Domain/MIT License conditions described here, as they choose.
The MIT License is about as close to Public Domain as a license can get, and is described in clear, concise terms at:
http://en.wikipedia.org/wiki/MIT_License
The full text of the MIT License follows:
======================================================================== Copyright (c) 2007-2010 Baptiste Lepilleur
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.
======================================================================== (END LICENSE TEXT)
The MIT license is compatible with both the GPL and commercial software, affording one all of the rights of Public Domain with the minor nuisance of being required to keep the above copyright notice and license text in the source code. Note also that by accepting the Public Domain “license” you can re-license your copy using whatever license you like.