Firefox

Firefox is widely regarded as the leading browser in support the latest web protocols for hypertext. As well, it is fast, small to download, feature rich, and free. Many web designers dream that one day everyone will use Firefox.
Get Firefox here.

Firefox will run on any computer and any operating system EXCEPT Macintosh OS 9 and earlier.

For Macintosh OS 9, try one of these:

iCab is supposed to be pretty current, even on very old macs: http://www.icab.de/index.html
Mozilla, makers of Firefox, have an archive of older versions. Version 1.x worked in Mac Os 9: look for it here.
Netscape 6.2, available at the "download archive" section of Netscape.com