Rappture is a freely available, open source package. You can do virtually anything you like with it, such as modifying it, redistributing it, and selling it either in whole or in part. But you can't prevent anyone else from doing the same, and you must keep all copyright notices intact, so the ownership and authorship is clear.
The license terms for this package are described in the file license.terms included in the source distribution. See the current source distribution for the latest copy of the license terms.
Here is a recent copy, not guaranteed to be the very latest:
Copyright (c) 2004-2012, Purdue Research Foundation All rights reserved. Developed by: Network for Computational Nanotechnology Purdue University, West Lafayette, Indiana http://rappture.org 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 the Network for Computational Nanotechnology, Purdue University, 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.