"Compatibility and 3rd Party Extensibilty
- Record and Replay Virtual Machine Execution — ESX/ESXi 4.0 provides the ability to record and replay the execution of a virtual machine for forensic or debugging purposes. APIs enable third parties to control this functionality.
- MODIFIED Additional Guest Operating System Support — ESX/ESXi 4.0 adds support for guest operating systems not previously supported on the ESX platform. Support has been added for the following guest operating systems:
o CentOS 4
o Debian 4
o FreeBSD 6
o FreeBSD 7
o OS/2
o MS-DOS 6.22
o Windows 3.1
o Windows 95
o Windows 98
o Windows 2000
o Netware 6
o Red Hat Enterprise Linux 5
o OpenServer 5
o Unixware 7
o Solaris 8 (experimental)
o Solaris 9 (experimental)
o Solaris 10
"
Source: Anonymouse