Penny's OS 2.0 (S 21)

or UberOS or UbixOS
or ubuntu or ubuntu eee
or ubuntu JeOS or ubuntu Lite
or ubuntu Minimal Desktop or ubuntu Mini Remix
or ubuntu Mobile or ubuntu Netbook Edition
or ubuntu Privacy Remix or ubuntustudio
or UCLA Locus or UCLA Secure
or uClinux or UCS

or UCSD-p or or udos 

or Ufficio Zero or UHC

or UHU-Linux or UKnow4Kids
or uL or U-lite
or Ulteo or Ultima

or Ultimate or ULTRADOS
or Ultrix or Umax 

or UMD or UMES
or Umix or UMMPS

or UMN or Underground
or uNETix or Unicos
or Unicox-max or Unics
or Unifix Linux or UniFLEX
or UNI/OS or UniPlus
or Uniq or UniqueOS

or Unison/Reliant pSOS or Unison RTOS 

or Unisys or Unisys OS 2200
or Unisys U5000 or Unity
or UNIX or UNIX-RTR 

or Unix System III or UNIX 32M
or UNIX Time-Sharing System or UnixWare
or UNOS or UNSW
or Unununium or U-OS 

or Urli OS or UserLinux

or USG or USIX

or USS or USX 

or UTEK or UTILEX 

or UTS or Ututo 

or UTX-32 or ux 

or UXP/DS or UXP/V

or UZIX