let me count
10.
Ubuntu 11.10 + Windows 7 Ultimate
Ubuntu 11.10 + Windows 7 Ultimate
Ubuntu 12.10 + Windows 7 Ultimate
Ubuntu 12.10
Ubuntu 12.04
Ubuntu Server 12.10
MS-DOS 4.01
Windows Server 2008
Android 4.2.1 (AOKP)
Android 2.2.2
-some weird old closed dumbphone OS by LG-
OpenELEC (XBMC for Raspberry Pi)