Racket is distributed under the GNU Lesser General Public License (LGPL).
Our primary goal is to help as many people as possible use and contribute to Racket. We encourage anyone to develop any kind of software, with any kind of license, using Racket.
We have chosen the LGPL as the license for Racket, which makes it possible for for people to create software with Racket, and to allow us to build on existing libraries that use the LGPL, such as the Lightning assembler and the GMP math library. The basic requirement of the LGPL is that you make your changes to Racket available, and that you let other people use your software with new versions of Racket.
Since the LGPL license that Racket uses was originally designed for C programs, parts of it require some interpretation to apply to Racket in detail. The following is how the Racket maintainers interpret the license.
First, if you distribute your Racket application in source form or as compiled bytecode files, the Racket license does not restrict you at all.
Second, if you distribute your Racket application as compiled binary generated by raco exe, there are no requirements placed on the licensing of your software. However, the LGPL requires that you make it possible to re-link your software with modified versions of Racket. This means, basically, that you need to provide the compiled bytecode files used to produce the compiled binary, if requested by someone who got your software from you. Note that this does not mean that your software has to be made open source, nor do you have to give the source code to anyone, nor do you have to make the compiled bytecode files available to the public or let other people redistribute them. Furthermore, this is not revealing any more of your source code than the raco exe format, since the bytecode is embedded in an extractable way in the resulting executable.
We are, of course, not lawyers, and this should not be taken as legal advice. However, we wanted to make it clear that Racket is an appropriate building block for all kinds of software, and to clarify how we view the license of Racket.