Yes. Parts are GNU software (gcc, gas, ld, etc.), parts are covered by the standard X11 license, some of it is public domain, some of it was written by Red Hat and placed under the GNU General Public License (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 for more information on how the GNU GPL may affect your use of these tools. If you intend to port a proprietary application using the Cygwin library, you may want the Cygwin proprietary-use license. For more information about the proprietary-use license, please go to http://www.redhat.com/services/custom/cygwin/. Customers of the native Win32 GNUPro should feel free to submit bug reports and ask questions through Red Hat channels. All other questions should be sent to the project mailing list <cygwin@cygwin.com>.