Can I bundle Cygwin with my product for free?
Only if you comply with Cygwin’s license very carefully. If you choose to distribute cygwin1.dll, you must be willing to distribute the exact source code used to build that copy of cygwin1.dll as per the terms of the GPL. If you ship applications that link with cygwin1.dll, you must either provide those applications’ source code under a GPL-compatible license, *or* purchase a cygwin license from Red Hat.