WxExtLib is available under a Zlib-like license:
COPYRIGHT NOTICE: WxExtLib library Copyright (c) 2003-2007 Daniel Käps The WxWidgetsExtensions library and associated documentation files (the "Software") is provided "AS IS". The author(s) disclaim all warranties, expressed or implied, including, without limitation, the warranties of merchantability and of fitness for any purpose. The author(s) assume no liability for direct, indirect, incidental, special, exemplary, or consequential damages, which may result from the use of or other dealings in the Software, even if advised of the possibility of such damage. Permission is hereby granted, free of charge, to any person obtaining a copy of this 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: 1. The origin of this source code must not be misrepresented. 2. Altered versions must be plainly marked as such and must not be misrepresented as being the original source. 3. This Copyright notice may not be removed or altered from any source or altered source distribution. End of WxExtLib library Copyright Notice
Additionally, some files are placed in the public domain. These are:
Note that when linking against wxWidgets libraries, wxWidgets Library License must be considered as well, of course.