Gqrx is distributed as source code as well as binary packages for Mac OS X and various Linux distributions:
On other Linux distributions please check the package repositories – Gqrx may already be available there.
On Mac you can also install the latest version through Macports.
Gqrx is now included in the PothosSDR bundle for Windows, although this is not officially supported by gqrx devs.
The source code is managed on Github: https://github.com/csete/gqrx