Yes. Parts are GNU software (gcc, gas, ld, etc...), parts are covered by the standard Berkeley license, some of it is public domain, some of it was written by Cygnus and placed under the GPL. None of it is shareware. You don't have to pay anyone to use it but you should be sure to read the copyright section of the FAQ more more information on how the GNU General Public License may affect your use of these tools. If you intend to port a commercial application using the Cygwin library, you may want the Cygwin commercial license that comes with the supported native Win32 GNUPro product. For more information about the commercial-use license, please contact info@cygnus.com. Customers of the native Win32 GNUPro should feel free to submit bug reports and ask questions through the normal channels. All other questions should be sent to the project mailing list cygwin@sourceware.cygnus.com.