L-to-R:Harvard Mark II
-tan (early computer used by the US Navy)Harvard Mark IV
-tan (early computer used by the US Air Force)
Apache HTTP Server-tan (most popular server software, described by The Art of Unix Programming as Linux's killer app
-- that is to say, the application that gained Linux its huge foothold in the server market. As such, Apache-tan is Linux-tan's trusted sidekick-thingy and BFF).
Next up, we have a couple of hardware-tans: Aluminum iMac
-kun and the floating display iMac
More info on these characters (and explanations of their designs) will be posted at this thread [link]