VirtualBox by InnoTek is a general-purpose full virtualizer for x86 hardware. It supports Windows (up to Vista), Linux distributions based on kernel 2.4 or 2.6, and OpenBSD as guest operating systems.
I only host precompiled binaries of the Open Source Edition (OSE). Those packages are dedicated to Mandriva Linux for x86-64. I don't have any 32-bit Linux system anyway. Here is a (reduced) list of upstream changes worth mentioning:
<Host>-<Fn> as <Ctrl>-<Alt>-<Fn> (Linux guest VT switch)