The Cobalt line of Linux-based hosting appliances is gaining new users following the decision by Sun Microsystems to open its source. More than 918K sites are currently running Cobalt, up more than 47K since November, when Sun announced it was discontinuing its last remaining Cobalt product, the RaQ 550 server.

In December, Sun released the ROM source code for the RaQ 550 under a BSD-style license, a year after open sourcing the Cobalt Qube code, which is now maintained by the Cobalt Users Group community as Blue Quartz. Prior to Sun's Christmas Eve announcement, the number of sites on Cobalt had been in steady decline from a peak of 3.1 million hostnames in August 2002.

While many hosting companies are phasing out the use of Cobalt since it officially reached its end-of-life on Feb. 19, others continue to see growth in the number of active sites running on Cobalt. A notable example is VIA Net.Works, which has seen 50 percent growth in sites on Cobalt at its newly-acquired Amen Hosting unit. Among those scaling back are two hosts who had some of the largest Cobalt installations prior to Sun's end-of-life announcement, Host Europe and EV1Servers.

Opening the source allows users to customize their own Cobalt "clones" with a lower cost of ownership. Cobalt became popular with hosting companies for their compact 1U design and user-friendly interface. Sun's acquisition of Cobalt Networks in 2000 was seen as providing a rapid entry into both the Linux and server appliance markets. But Sun struggled to position Cobalt, and new products from hosting automation vendors made accessible control panels more widely available. In January 2003 Sun took a $1.6 billion charge to its earnings to reflect the decreased value of the Cobalt acquisition.