Unfortunately EclipseCrossword is only available for Windows so you cannot install it directly on OSX on a Macintosh computer without the use of third party software. This leaves you a couple options if you only need to view the .ECW files including installing EclipseCrossword via third party software on the Macintosh or have someone with a Windows computer convert the ECW file to a format you can view more easily on your Mac. Below I describe each option in more detail.
Someone asked me how to open .ecw files earlier today. After a little research I was able to find out that the files were associated to EclipseCrossword which is crossword puzzle software. Below are instructions on how to install Eclipse Crossword Puzzle, open the .ecw file, and export the file to something that MS Paint or Microsoft Word can open.