If you can clarify what specific feature you need (e.g., "calculate illuminance," "export to CAD," "3D furniture import") and whether you mean a genuine free edition or a particular tool inside DIALux evo, I can give you a much more accurate answer.
As of this writing, version 8.2 is the latest stable release. Click the download button for (note: DiaLUX Evo does not run on Mac OS natively; Mac users need Parallels or Bootcamp). dialux evo 82 free