Quantum Composer is currently available as a free download for Windows, Mac OS X and Linux
Download for Mac OS X
Mac OS X 10.9 to 10.13
NB: You can download Composer for Windows and run it with Wine on versions that are not supported.
Download for Windows
Download for Linux
Ubuntu 16.04 LTS
NB: You can download Composer for Windows and run it with Wine on other Linux distributions and other Ubuntu versions.