It was fun troubleshooting Font issue on Mac. Follow the link given below to see how Nicholas Shanks help you read Kannada on your Mac Safari browser. The only font which is currently working on Mac to render Kannada text is found here.

Unicode Kannada Font & Keyboard Layout for Macintosh

Rendering issues: Mac vs. PC vs. Linux (Source)

Many kannada fonts are unsuitable for use with Macintosh computers, because they make use of OpenType technology, developed jointly by Microsoft and Adobe, for displaying vowel signs (matras) and ligatures appropriately. While OS X also recognizes OpenType layout tables, it uses a different rendering engine (ATSUI), and these fonts are written for Microsoft’s engine (called Uniscribe).

There is currently no built-in Kannada support in OS X. However, a font and keyboard developed by Nick Shanks is available from here.

We have lots of fonts which are compatible with most distributions of Linux running Gnome or KDE.  ttf-kannada-fonts is bundled with most of the distributions to offer Kannada fonts. They also include Kannada language packs with Keyboard layouts, input methods etc.