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MicroNet is a very useful script to people that want to show different material to a visitor depending on what browser (s)he uses. This script can also be used as a redirection script, depending on how you call it. A great editor is included which allows you to customize redirections based on what MIME type is displayed. This is a great tool for any content-based action.
Price: Freeware

This is a very very simple script that selects which style sheet to use based on which browser a visitor is using. It can also be used to seemlessly redirect users based on their browser to specific html pages. Requires SSI.
Price: Freeware