The current 0.6.0 release contains only Windows GUI. Linux and OSX support are a work in progress. Lots of stuff implemented, lots still missing. You can download qtxie's branch with the WIP code here -
https://github.com/qtxie/red/tree/MacOSX-GUI?files=1
Read the Readme file for instructions on how to compile red code using sources. For any questions -
https://gitter.im/red/red