OpenOffice is a suite of office-specific software similar to Microsoft's Office suite, except that it is free and works across various platforms -- versions of OpenOffice can run on Windows, Mac OS X, Linux and even Solarix. The suite can also open and edit Microsoft Office documents such as .doc and .xls files. The default spreadsheet file type for the OpenOffice spreadsheet application is .ods. Install the OpenOffice suite in order to open .ods files on your Mac.
Download the OpenOffice version for Mac from openoffice.org. When you navigate to the site, it recognises your operating system and recommends the correct version; if the auto-recognise is wrong, check for other versions at download.openoffice.org/other.
Double-click the downloaded .dmg file to mount the disc image.
Open the mounted image and drag the OpenOffice application into your Applications folder. OpenOffice is now installed.
Start OpenOffice. In the welcome splash screen, click "Open a document..." Navigate to the location of the .ods file you wish to open, and click "Open."