These companies were lucky enough to register them before December 1, 1993 (or buy them from someone who registered them by that date), as the Internet Assigned Numbers Authority put a restriction on single character domains at that time.
o.co and o.info are both owned by Overstock.com (OSTK).
q.com is owned by CenturyLink (CTL). If you go to q.com, it takes you right to CenturyLink's web site.
x.com is owned by x.commerce, which is owned by eBay (EBAY). When you go to the x.com website, it takes you to the x.commerce website.
z.com is owned by Nissan North America Inc., which is owned by Nissan Motor (NSANY), which trades on NASDAQ. However, the website is currently inactive.
i.net is owned by Future Media Architects, a privately held company.
u.tv is owned by UTV Media (UTV.L), a broadcasting and New Media company based in Belfast in Northern Ireland. The company trades on the London Stock Exchange.
Want to know all the companies that have one letter stock ticker symbols? Here they are:
Agilent Technologies Inc. (A)
Barnes Group Inc. (B)
Citigroup, Inc. (C) formerly the symbol for Chrysler
Dominion Resources, Inc. (D)
Eni SpA (E)
Ford Motor Co. (F)
Genpact Ltd. (G) formerly the symbol for Gillette
Hyatt Hotels (H)
Kellogg Company (K)
Loews Corporation (L)
Macy's, Inc. (M)
NetSuite, Inc. (N)
Realty Income Corp. (O)
Pandora Media (P)
Ryder System, Inc. (R)
Sprint Nextel Corp. (S) formerly the symbol for Sears Roebuck
AT&T, Inc. (T)
Visa, Inc. (V)
United States Steel Corp. (X)
Alleghany Corp. (Y)
Zillow (Z) formerly the symbol for Woolworth, now known as Foot Locker (FL)
Before US Airways Group was delisted, it used to have the stock symbol U.