With free VMWare player it's possible to test your Java and web applications in almost any OS.
Here you can download different Linux OS distributions pre-configured with different software, such as CRM, firewall, web browsers, free web/email/collaboration servers, SSL VPN, security tools:
My favorite is Linux OS configured with several web browsers, which makes it possible to see how web (Domino) applications look like in Linux's browsers:
I've heard (blink blink ;)) that there is even a way to run Mac OS X in VMWare in Windows. If it was true, that would be a great way to test how web (or Java) applications work in Mac OS.