Reverse Proxy solution for exposing Client Access Server (OWA, Outlook Anywhere...) other than MS Solution

Many folks have used ISA Server, TMG, and now UAG as reverse proxy to expose OWA, Outlook Anywhere and so on.

I am looking for known working alternatives that provide the same functionality.

I am not looking to debate whether to use a non MS solution or MS solution, but alternatives that are known to work.

Perhaps a Virtual Appliance.

Thanks for your input.